Abstract: Ecological security is the prerequisite for sustainable development of society and economy. It is of great significance to study the historical evolution and development trend of regional ecological security. An ecological security evaluation index system was established based on PSREES model. The comprehensive index method was adopted to calculate the ecological security values of five cities in the Hexi Corridor urban agglomeration from 2008 to 2017. ARIMA-ANN composite model was used to predict the future trend of regional ecological security. The ecological security in Hexi Corridor showed a fluctuating and rising state. The evolution characteristics were consistent with the regional ecological protection planning and policy. The ecological security level of each city was different from the ideal state. The security value of pressure layer in Zhangye, Jingchan and Jiuquan were relatively low, with some potential ecological risk. The ecological security trends in the Hexi Corridor urban agglomeration were predicted using ARIMA model and ARIMA-ANN model, with the results showing the average relative error and correlation coefficient of 2.01%, 0.8852 (ARIMA), and 1.09%, 0.9665 (ARIMA-ANN). Moreover, the ARIMA-ANN composite model predicted that ecological security value of Hexi Corridor would reach 0.8107 (level V) in 2020. This study verified the high accuracy and precision of ARIMA-ANN composite model for evaluating regional ecological security evolution and predicting development trend. It is of vital practical value for the optimization of regional ecological spatial layout and security management.

Key words: aggregate stability, soil aggregate, returning from cropland to tea, inorganic phosphorus fraction.