In order to improve the shortcomings of traditional decision threshold technology in free space optical communication (FSO) system and reduce high cost loss caused by that reference light do not carry any information in continuous wave reference light assisted detection technology, an adaptive decision threshold (ADT) technique is proposed that the current code decision threshold is obtained based on the quantized voltage of judged signal previously. The direct current (DC) component in extracted signal is used as continuous wave (CW) reference light to estimate the fluctuating characteristics of atmospheric turbulence channel. Results show that under the condition of bit error rate of 10－3, the adaptive decision threshold and DC extraction technology have lower power loss, which can significantly improve the performance of FSO communication systems.