Abstract: Using the Severe Weather Automatic Nowcast system (SWAN), SWAN product characteristics are analyzed, and its early warning and forecasting indexes are summarized based on an extremely heavy rain event that took place in the Shali river basin, Henan province during 4-5, July 2012. The results are as follows. (1) The stations where precipitation exceeds 30 mm h-1 corresponds 97.4% of one-hour maximum reflectivity factor over 45 dBz, and 84.6% of echo top over 11 km. Reflectivity factor is a significant indicator for short-time strong rainfall forecasting. (2) The area of high vertical integrated liquid water content (VIL) and the area of precipitation over 10 mm h-1 have a great correlation. (3) Quantitative precipitation estimation (QPE) has a good skill to evaluate the precipitation over 30 mm h-1. (4) Quantitative precipitation forecast (QPF) often underestimates the precipitation over 30mm h-1, and the average QPF error is smaller than 30 mm. (5) The echo movement vector (COTREC wind field) can denote the storm future movement direction, and the one-hour heavy precipitation center and the echo movement vector convergence zone have some corresponding relationship.