Morlet wavelet transform of precipitation in Hetao area during April to May shows that there exist three obvious periods:7 ,24 and 3 year.The 7 year period is the strongest. Precipitation tendency of April May in this area is expected to be negative anomaly in 2000~2003,and obvious drought in 2000,and obviously positive anomaly in 2004(or 2005) by using Morlet wavelet analysis and Periodogram method.