In the coherent optical communication system, the traditional blind phase search (BPS) algorithm has shown its excellent tolerance to laser linewidth, however its high-computational-complexity limits its practical applications. Thus a low-computational-complexity carrier phase estimation (CPE) algorithm is proposed, in which the phase-test range is defined based on the slow variance characteristic of noise phase produced by laser linewidth and the optimum phase angle is searched. Consequently, the number of phase searches is finally reduced and the computational complexity of this algorithm is also significantly reduced. Meanwhile, the proposed algorithm can avoid the problem of few phase mismatches existing in the traditional BPS algorithm and thus it is superior to the traditional BPS algorithm in performances. Finally, the correctness and validity of this algorithm are verified in the polarization multiplexing coherent optical communication system.