Based on the conventional observation data, FNL reanalysis data and radiosonde data, this paper makes a comparative analysis of the rainstorm forecast errors under the cold air background from June 7 to 9 and From July 26 to 29 in 2020. The results show that: 1. The circulation background of the two processes is similar, with cold air, vortex and shear line coordination, and the strong southwest jet did not form in the two processes. However, due to the difference of cold air intensity, influence time and thickness, the empty or missing report of rainstorm was caused: During the process of "6?8", weak cold air was driven by easterly wind to penetrate southward slowly, which was conducive to the occurrence and maintenance of local heavy rain under the background of the topographic action of windward slope and the strong development of warm trough northward. The cold air of "7?26" affected too early and too strong, resulting in the location of the surface convergence line to the south and the real rain belt to the south. In addition, the cold air obstructs water vapor transportation to the north, which is one of the reasons for the empty forecast of heavy rain in northern Hunan. 2. The atmospheric environment field in the "6?8" process is unstable, and there are certain water vapor conditions and lifting conditions, which are sufficient conditions for the occurrence of disastrous weather. The potential conditions for predicting the location and time of disasters are difficult to be reflected from the existing observation data, making the prediction more difficult. 3. The strong cold air force of "7?26" is also manifested in the strong cold advection in the middle layer and the existence of a downdraft, which is not conducive to the occurrence and development of strong convective weather. Under the seasonal environmental background, forecasters need to make forecast corrections according to the intensity, path and influence time of the adjacent cold air.