Research of loss of coolant accident (LOCA) postulated on the nuclear reactor coolant system (RCS) was investigated with ANSYS program. Secondary development of ANSYS was performed to form the customized module for implementing effective and efficient RCS LOCA nonlinear analysis. A standard analysis procedure was established. It has following functions, such as parameters and modular system modeling, automatically set break, static pilot analysis, LOCA nonlinear dynamic calculation and automatic reports generation. Main pipes, Steam generator and reactor coolant pump models were molded by parameterized modular modeling method. Those models considered the nonlinear factors, such as material nonlinearities, gap and so on, constructed component model libraries of RCS. Comparing the results calculated by ANSYS and program-specific, it is showed that the results are generally consistent.