Based on the Ji'nan S-band dual-polarization Doppler weather radar (CINRAD/SA-D) data, combined with automatic weather station data and conventional observation data, comparative analysis of the environmental conditions are made, and emphasis is laid on the analysis of dual-polarization signatures for the Wangzhuangji storm and Da'an storm, which are short for the two extreme rainfall storms separately occurring at Wangzhuangji county of Shenxian and Da'an county of Yanzhou, Shandong on 5 and 6 August 2020. The results show that: the two extreme heavy rain occurred in the conditions of high K index, large convective available potential energy (CAPE), deep wet layer, and moderately weak vertical wind shear. In contrast, the storm relative helicity (SRH) is evidently larger for the extreme rainfall event on 6 in August. The flow structures of the storms are significantly different: the Wangzhuangji storm tilts upward and intensively diverges at high-level inducing higher storm top and specific differential phase K_DP column, while Da'an storm performs as cyclonic rotation with weaker high-level divergence. The microphysical structure varies at different levels: for the both two storms, there are high concentration of solid (liquid) particles separately above (below) -10 ℃ layer. But Wangzhuangji storm has more abundant graupels above -10 ℃ layer, a few element of liquid particles from -20 ℃ to -10 ℃ layer, and a certain amount of ice particles below -10 ℃ layer. The two storms exhibit comparable dual-polarization characteristics with moderate differential reflectivity Z_DR, bigger K_DP and correlation coefficient (CC) at low-level, which indicate that the rainfall storms constructed with abundant moderate particle size liquid raindrops are rich of water favorable for extreme rainfall.