Based on the assimilation of radar radial wind, radar retrieval wind and GPS water vapor data with the ensemble Kalman filtering (EnKF) method, the initial water vapor field of a squall line that occurred on 30 July 2014 in eastcentral Anhui was adjusted according to radar reflectivity data. Compared with the simulation results of EnKF, this method has improved the simulation of intensity, location, duration, precipitation and surface wind of the squall line. Simulation performance of ground convergence zone in the front of the squall line was improved after adjusting humidity field, leading to better simulation results of the intensity and location of the squall line. In addition, the squall line maintained for a shorter time without humidity adjustment and the intensity was weak. This can be explained by the fact that midlevel dry air entrainment was weak in the rear of the squall line, and the cold pool moved quickly away from the squall line, which was unfavorable for the maintenance of squall line. In contrast, after the humidity field was adjusted, dry air entrainment in the rear of the squall line was strong, and the resultant downdraft generated the cold pool, which was located in the rear of the squall line, favorable for the maintenance of squall line. The possible reason for dry air entrainment strengthening tends to be that atmospheric instability was increased with the moisturizing of midlow level (600-900 hPa) after the humidity field adjustment, and the development of convection results in the enhancement of lowvalue system. The westerly in the south of lowvalue system intensifies, strengthening the dry cold air entrainment in the rear of the squall line. This experiment reveals that the adjustment of the humidity leads to the adjustment of the dynamic field, which plays an important role in the development and organization of the convection system.