The horizontal and vertical momentum loss caused by the shock of heavy rain in low-level wind shear of thunderstorms on the airframe and wing are analyzed,the water film thickness on the airframe and wings estimated,and the flight resistance resulted from raindrops-striking caused by the roughness of airplane when the heavy rain shocks the airplane is discussed.Study shows that the effect of the shock of heavy rain on an airplane in the low-level wind shear of thunderstorms is evident,the flight resistance resulted from the roughness of airplane is able to change the flight track and endanger the flight safety,whereas,the increase in the mass of airplane caused by the water film on the airframe and its wings in heavy rain is nigligible.