Abstract: Based on the in-depth study of second-order mechanism model of Lawrence-McCarty formula BOD soft sensor,Partial Least-Squares(PLS) method was used to compensate the error of the BOD model formula,and propose the soft sensor model of multi parameters for sewage treatment process.The simulation results show that the precision of mixed model value is improved,and it provides an effective way of measure BOD effluent quality sewage treatment process accurately,and also create the conditions for the real-time control of sewage treatment process.