The China Meteorological Administration Global Forecast System (CMA-GFS) has been upgraded to version 4.0 in May 2023. To evaluate the forecast capability and bias characteristics of CMA-GFS before and after the upgrade， this study compares and analyzes the performances of CMA-GFS， the Regional Numerical Weather Prediction System (CMA-MESO)， and the European Centre for Medium-Range Weather Forecasts (ECMWF) in predicting southwest low vortex-induced heavy rainfall events in Sichuan in 2022 and 2023. The comparative evaluation shows that: the CMA-GFS model underestimates the extreme heavy rainfall event；with the rainfall scores in 2022 significantly higher than those of ECMWF and CMA-MESO; while in 2023， the scores decreased and were slightly lower than those of ECMWF. A multi-dimensional evaluation and diagnostic analysis of CMA-GFS was conducted for a typical southwest low vortex case from July 26-28， 2023， including the circulation pattern and low vortex system. The results indicate that: the position and movement of the main influencing system forecasted by the CMA-GFS 4.0 model are consistent with the observation， with accurate rainfall location prediction， offering useful guidance for the low vortex heavy rainfall events; the forecasted wind speed is significantly underestimated from the initial field， especially the component of southward wind， leading to an under forecast of the low-level jet stream， implying that the weak dynamic forecast associated with wind speed is a major factor for the underestimated rainfall intensity; the underestimation of low-level energy and instability conditions are related to the dry bias in the lower atmosphere， resulting in weaker convective intensity and shorter duration; Biases in the early stages of the southwest low vortex are relatively prominent， but the biases decrease and even reverse during the peak stage of the vortex.