H.264 video decoder is a good choice for embedded video processing applications because of its higher compression ratio than MPEG2, although it has higher requirements of run-time computational resource. Multi-core system is the future of the embedded processor design for its power efficiency and multi-thread parallelization capability, and can be used to fit well with the requirements for such video processing algorithms. To simulate and evaluate the performance of these multi-core systems effectively, a design flow at the system level is developed, at the higher level, the combination of TLM language (SystemC) and shared-memory parallel programming model (OpenMP) is used for such transaction-level simulation, and at the lower level, a multi-core simulator based on the extension of the SimpleScalar 3.0 ToolSet is developed for the cycle-accurate level simulation. Compared with other high-level simulation methods, ours has the ability to realize the true-parallelization simulation. What is more, experiments show that such simulation methodology can effectively simulate these complex multi-core applications in a short time to get the appropriate core number and the task allocation strategy (much less than RTL-level simulation) and the results can get at less than 15% deviated from the ideal ones calculated based on Amadal's Law, so the parallelization strategy obtained from such simulation is the best one that can be further applied for the RTL-level design of the final multi-core system.