An improved Blind Phase Search algorithm was proposed. In this algorithm, carrier phase noise was estimated by searching minimum Euler distance twice. To verify this algorithm, an optical linear sampling simulation system was set up. The constellation diagram of 10Gbaud/s 16QAM signal was simulated by using an optical frequency comb with pulse width of 500fs and duration of 10ns as optical sampling source. The simulation result shows that, the phase noise between the signal source and optical sampling source can be compensated effectively by this algorithm when the sum linewidth of the two lasers is less than 10MHz. Finally, the constellation diagram of 10Gbaud/s 16QAM signal is displayed clearly.