Based on the analysis of the structure of regional ecological system, the three-level index system for assessing regional ecological security is put forward, including guide layer, first-level index layer and second-level index layer. The guide-layer which based on P-S-R model can be divided into four parts: ecological system status,social pressure, environmental pressure and social response. The construction of multi-level evaluation model is introduced and regional ecological security in Tongchuan city is evaluated. The result shows that ecological security in Tongchuan city is in critical status.