In view of shortcomings of Benchmark simulation model no.1 (BSM1) , such as time consuming, complicated structure and hard to research and optimization, a model based on LSSVM (least squares support vector machine) for sewage treatment process is presented. Introduces BSM1 firstly, then establishes LSSVM-based simplified model of sewage treatment process on BSM1, finally compares the simulation results of BSM1 and LSSVM-based model. It indicates that the LSSVM-based model has higher operation efficiency.