The ENSO cycle is a strong signal in atmosphere-ocean interaction,and plays a significant role in the global climate,including the East Asia monsoon region.Typically,in the developing phase of El Niño,the convection is strong in the east-central tropical Pacific,and weak in the west tropical Pacific and Maritime continent.In the following summer,the northwest subtropical high is weaker than normal,and is located southward from its normal position.As a result,the southwest jet stream from the Bay of Bengal is weaker than normal,and carries less moisture to mainland China.In the decaying phase of El Niño,the Philippines anti-cyclone can persist until summer,and the northwest subtropical high is strong and located westward from its normal position.The southwest jet stream from the Bay of Bengal is much stronger than normal and carries more moisture to mainland China.In addition,the Yangtze River typically experiences flood events.Aside from the ENSO cycle,the vertical averaged eddy temperature difference between the Asian and Pacific may have less influence on the East Asia summer monsoon.The Asian-Pacific Oscillation(APO) and its associated indexes can be used to identify this difference.With higher APO index years,in the upper troposphere the summer South Asian high and North Pacific trough are stronger,while the westerly jet stream over Asia and easterly jet stream over South Asia are strengthened.Further more,in the lower troposphere the Asian low and North Pacific subtropical high are stronger.The anomalous westerly prevails over South Asia,and the Meiyu front is located northward from its normal position.Such a circulation pattern may lead to greater rainfall in northern China,southern China and South Asia.Further analysis shows that the combined impact of the ENSO phase and APO index has different predictability for the East Asia climate.This paper will study the 2015/2016 monthly prediction skill differences under the background of super strong El Niño events and different APO index conditions.The data used in the paper include station precipitation data,BCC_DERF2.0 hindcast and forecast data,NCEP/NCAR reanalysis data,and the scores of NCC issued monthly precipitation forecast.Some of the results are obtained through verification methods and diagnostic techniques,as follows:(1) During the super El Niño event occurring from 2015 to 2016,the skills of the issued monthly precipitation prediction are high/stable in 2015(El Niño developing phase),and low/unstable in 2016(El Niño decaying phase).The skills of the key circulation predicted by BCC_DERF2.0 show results similar to the precipitation.Further analysis indicates that Asia-Pacific Oscillation(APO) may play another important role in the predictability of monthly scale prediction in 2015 and 2016.(2) The APO index is low in summer 2015 and high in summer 2016.The effect of low APO on East Asia circulation is consistent with that of the El Niño developing phase in 2015,while that of the high APO on East Asia circulation is not consistent with that of the El Niño decaying phase in 2016.That is to say,the eddy temperature difference between the Asian and Pacific in 2016 is favorable for strong Asia summer monsoons,while the El Niño decaying phase leads to weak summer monsoons.(3) The circulations in 2016 show some typical features of higher APO index conditions,and BCC_DERF2.0 can predict most of the features of the high APO index conditions in 2016.The summer rainfall anomaly in 2016 shows that both the Yangtze River and northern China experienced flood disasters.These facts imply that the climate features in 2016 are multi-factor results.(4) The combined effect of the APO index and El Niño phase may have different predictabilities on the monthly East Asian circulation.The skill of BCC_DERF2.0 depends on these two factors,as does the monthly precipitation in 2015 and 2016.