As a part of hydrokinetic energy conversion systems, bidirectional impulse turbines are used in oscillating water columns (OWCs) to extract wave energy. Transient numerical simulations were implemented to predict the unsteady behaviors of reciprocating airflow. Firstly, the effects of blade thickness, blade rotation angle, and blade incident angle on the aerodynamics performance were investigated, and results shows that blade thickness has a slightly influence on turbine efficiency under steady-state condition, however, both the decrease of the rotation angle and the incident angle significantly increased the turbine efficiency. An efficiency peak of 57% was achieved with alpha= -6° and a flow coefficient of 1.0. Secondly, and pressure fluctuations of an impulse turbine were analyzed under sinusoidal flow, which shows that the energy loss of the turbine is attributed to the vortex generated near the downstream guide vanes. It is also shown that the pressure fluctuation is mainly caused by the unsteady incident wave, moreover, the pressure fluctuation frequency of blade surface is near to the incident wave frequency or a multiple of the incident wave frequency.