Using the statistical yearbook, rural yearbook and bulletin of soil and water conservation data in Gansu Province, based on the pressurestateresponse (P-S-R) model, 12 evaluation indexes were selected to construct the ecological security evaluation system and to evaluate spatial ecological safety in Gansu Province. The results showed that: (1) Significant changes had taken place in the three major indexes in the study area in past 26 years. The average contributions of condition indicators, response indicators, and pressure indicators were 30%, 27.5%, and 42.5%, respectively. (2) The ecological safety shifted from 0.31 in 1986 to 0.67 in 2011 based on the analysis of three major river basins. The ecological safety had improved, but the task to guarantee the ecological security is still very arduous. (3) The average ecological safety ranged from 0.36 to 0.58 in 14 cities (prefectures) from 1986 to 2011. The overall ecological safety was at Ⅲ and Ⅳ levels in the whole study area. The ecological safety of Tianshui was higher and relatively stable; however, other regions should strengthen environmental protection based on the current situations, ensuring the regional ecological security.