Abstract: Based on the concept of urban ecological security（UES）,the UES assessment indicator system of Pingliang city is established according to PSR（pressure-state-response） model. UES assessment model was proposed from structural evolution of complex systems based on the maximum information entropy principle（MIEP）,self-organizing feature map neural network（SOFM） algorithm and MATLAB mathematical software. The UES status of Pingliang city showed that an increasing trend from 2002 to 2011. In 2002-2009,The UES of Pingliang city was in critical security,and improved in 2010-2011,2010 and 2011 was safer,in 2011 reached the highest value of 1.372 6,but there was still a gap with the ideal level of safety.

Key words: urban ecological security, pressure state response（PSR） model, maximum information entropy principle（MIEP）, Pingliang city