To satisfy requirements of complex system modeling and simulation, an M&S approach of combining SMP2 and SOA is improved. Aiming to implement SMP2-based simulation under SOA, four aspects of SMP2 are studied: 1) service-oriented distributed simulation system architecture is propounded. 2) Component interfaces related to the model composition and schedule are redefined. 3) Simulation model service description is added to the Simulation Modeling Define Language which is called SMP2 metamodel. 4) Modeling and simulation process for SMP2 under SOA is detailed. Finally, a SOA-based modeling and simulation environment for SMP2 is designed and implemented, and an example of Navigation System's Service Performance analysis simulation is given to demonstrate the validity and feasibility of the method.