This paper proposes an adaptive switching gain complementary sliding mode control (CSMC) for Permanent magnet synchronous motor (PMSM) speed control. First, the equivalent control law is designed for PMSM speed loop using the CSMC theory. Then, to avoid the need of calculating an upper limit of the system uncertainties, the new adaptation law and hitting control law are developed. Theoretically, the proposed method ensures the switching gain adjust to the upper bound of the system uncertainty using the complementary sliding variable. Compare to the conventional adaptive approach, the proposed one can adjust the switching gain bi-directionally and suppress the chattering phenomenon significantly. At the same time, the stability of the proposed control scheme is verified in this paper. Finally, the effectiveness of the proposed control approach is illustrated using some experimental results.