Maintaining an adequate security level of cultivated land is essential for the healthy and sustainable survival of China's large and growing population. We constructed a cultivated land security evaluation index system, combined with an improved TOPSIS method by taking into account the balance and stability of quantitative, qualitative, and ecological security. We applied this improved method to an evaluation of the state of cultivated land security and analyzed its spatiotemporal variation in Yingtan City (Jiangxi Province, China) from 1995 to 2015. The drivers of the changes in cultivated land security were investigated via a spatial regression model, which can eliminate the effect of spatial autocorrelation. The results showed that cultivated land security decreased rapidly from 1995 to 2005, although it tended to rise slowly in the subsequent period from 2005 to 2015. Areas deemed to be in a highly dangerous state were mainly distributed in the Yuehu District, while those that were secure appeared primarily in the southern mountainous area, with the area in a generally dangerous state extending to the west in the same direction as urban development. Among the examined drivers, social-economic factors and policy factors significantly influenced the cultivated land security. Our work suggests that government managers should take appropriate measures to improve cultivated land security according to its spatiotemporal variations and the underpinning drivers in this region.