Abstract: In order to improve the symbol detection performance of an atmospheric laser optical frequency division multiplexing(OFDM) receiver, semi-blind estimation was carried out in an atmospheric laser OFDM time-varying channel by means of a mixed particle filtering algorithm. Comparing with the existing time-varying channel estimation based on pilot, this method can effectively improve symbol detection performance at receiver. Finally, MATLAB simulation proved the effectiveness of this new method. Obtained results show that this method can decrease bit error ratio to one magnitude at receiver under the same signal-to-noise ratio compared to other methods.