This paper develops a dynamic asset allocation model for pension funds with fixed contribution rates to study the optimal portfolio time paths, which minimize a fund's solvency risk. Data from the Civil Service Pension Fund as well as returns of various asset classes are used to simulate the interactions among the fund's funding ratio, asset returns and investment horizon. The simulation results indicate, Ⅰ) when a pension fund faces the under-funding problem, it should take an aggressive asset allocation strategy to speed up the accumulation of fund's asset. Ⅱ) The dynamic asset allocation technique can help a fund to reach a fully funded status in its later stage provided that the fund's funding ratio is within a reasonable range in the beginning. Ⅲ) A fund should be even more aggressive after experiencing big investment losses. Ⅳ) The shorter the investment horizon, the more conservative the portfolio should be.