Both the nozzle expansion ratio and the chamber pressure are simultaneously and continuously changed according to pintle movement, resulting in a different internal flow structure and flow separation characteristics. In this paper, the pintle position effect on nozzle flow structure and separation phenomena is analyzed by experimental-aided Computational Fluid Dynamic(CFD). Among the turbulent models for RANS(Reynold Averaged Navier Stokes) in Fluent, Spalart-Allmaras model is better agreement with the nozzle wall pressure distribution attained by cold-flow test than other models. And even if a conical nozzle is used, there is a shock structure similar to cap-shock pattern mainly occurred in contoured or shaped optimized nozzle because of internal shock generated from pintle tip flow separation.