In this paper, we propose a novel algorithm for compensating the common phase noise in coherent optical orthogonal frequency division multiplexing system. The proposed algorithm adopts the common phase noise blind estimation method which is based on the two-dimensional projection histogram,and a pilot-aided phase noise estimation method is combined, thereby realizing the effect compensation for the common phase noise. First, the common phase noise of frequency domain symbols caused by few comb-type pilots can be estimated initially and compensated. Second, by using the two-dimensional projection histogram, the constellation of received signals can be mapped in two-dimensional digital images, and the fine compensation for the common phase noise can be achieved. To verify the performance of our scheme, we build a 20 Gbit/s simulation system based on the commercial OptiSystem and MATLAB over 50 km standard single mode fiber transmission. The corresponding results show that, the proposed algorithm can solve the problem that the bias with period of π/2 exists in the projection histogram blind estimation algorithm. Compared to the traditional pilot-aided scheme, our scheme uses only fewer numbers of pilots and achieves better bit error ratio performance.