Taking a typical MTC (multiple tropical cyclogenesis) event in midsummer of 2018 as an example,this paper investigates the effects of multi-scale circulations (including large-scale circulation,intra-seasonal oscillation (ISO) and tropical waves) on MTC,and discusses the deviation of vertical disturbance field of the whole atmosphere in MTC active and inactive phases.The results are as follows.(1)The western North Pacific (WNP) undergoes a 16 d MTC active phase with eight tropical cyclones (TCs) generated in sequence and a 19 d MTC inactive phase with only one TC generated in midsummer of 2018.(2)During the MTC active phase,the cross-equatorial airflow strengthens,and the monsoon trough strengthens and extends eastward.The atmospheric circulation configuration of low-level convergence and upper-level divergence over South China Sea (SCS) and WNP is conducive to TC formation.(3)The northward propagation of ISO (intraseasonal oscillation) in East Asia and WNP in summer has a significant modulation effect on the sub-seasonal variation of MTC.The SCS and WNP are just in a northward wet (dry) phase of a strong ISO during the MTC active (inactive) phase.(4)The formation of eight TCs in the MTC active phase is all related to tropical waves,of which five are affected by two kinds of tropical waves simultaneously.Tropical waves provide triggering conditions for TC formation by changing the local thermal and dynamic conditions.(5)The combined effects of multi-scale circulation eventually leads to significant differences in the vertical structure characteristics of temperature-pressure disturbance field configuration,vertical motion disturbance and specific humidity disturbance in the MTC active and inactive phases.The application of the disturbance analysis method provides a new idea for MTC extended range forecast.