Understanding how compound heat and drought affect vegetation productivity is essential for ecosystem sustainability. However, current research has predominantly focused on larger spatial scales, particularly in humid and semi-humid regions, with comparatively less attention given to arid and semi-arid areas. Investigations integrating both compound heat and drought sequence and compound events to assess vegetation productivity responses remain limited. This study focused on the Wei River Basin in the arid and semi-arid regions of China, based on the Standardized Temperature Index (STI), Standardized Precipitation Index (SPI), Gross Primary Productivity (GPP) data, a meta-Gaussian model was used to quantify the probability of GPP decline under compound heat and drought conditions, and a typical compound heat and drought event (CHDE) was identified to assess the GPP loss. The results indicated that with the intensifying heat or drought conditions, the likelihood of vegetation productivity decline in the Wei River Basin increased notably. Under mild, moderate, severe, and extreme heat (drought) conditions, the average probabilities of GPP decline were 44% (63%), 47% (70%), 51% (74%), and 60% (80%), respectively. Notably, drought posed a greater risk of vegetation productivity reduction than that of heat. Compared to single heat or drought, compound heat and drought significantly increased the probability of vegetation productivity decline. Under compound mild, moderate, severe, and extreme conditions, the average probabilities of GPP decline were 63%, 71%, 73%, and 90%, respectively. As compound conditions intensified from mild to extreme grades, the probabilities of GPP decline increased by 8%, 10%, and 27%. During the typical CHDE occurred from May to October of 1997, the GPP value was lower than the normal levels throughout the whole period, and the more severe the compound event, the greater was the loss in GPP. The largest GPP loss occurred in August, reaching 31.03%. Among the different vegetation types, grassland and cultivated vegetation experienced the most significant declines of GPP (23.6%, 19.74%), whereas broadleaf forest and shrubland exhibited the lowest ones, with both under 9%. This suggests that we should pay more attention to grassland and crops during the CHDE, and take effective measures to reduce the GPP decline and then alleviate the carbon loss risk of vegetation ecosystem.