Traditional bottleneck diagnosis of production lines mainly relies on the designer's experience, theoretical calculation or data analysis after practical system run. There are some disadvantages of the traditional bottleneck diagnosis for production lines. Using the virtual manufacturing technologies, a novel Simulation Diagnosis methodology about the Bottleneck of Production Lines (SDBPL) has been presented. With the proposed method, an existed production line is modeled, simulated and analyzed. Its bottleneck is quickly diagnosed by some ways such as visual simulation results, cycle time, machine utilization and labor utilization. Results reveal that SDBPL can find the location of bottleneck in the practical production lines without wasting practical resource because the entire course of the diagnosis for bottleneck is implemented in virtual environment, and SDBPL is quicker than that of traditional methods as well.