Abstract: The process of magnetic reconnection in an anisotropic plasma is studied based on two and half dimensional hybrid simulation. The results agree with theories. It is found that the growth rate of instability is enhanced greatly and the speed of magnetic reconnection is increased in the presence of pressure anisotropy （P_⊥/P_∥ = 1.5） compared with that in pressure isotropy. In a pressure anisotropy （P_⊥/P_∥ = 0.6） fire hose instability appears, which will restrain the tearing mode instability and magnetic reconnection. Because of the fire hose instability and the restraint of the tearing mode, the width of magnetic island in a pressure anisotropy （P_⊥/P_∥ = 0.6） is narrower than that in pressure isotropy. In addition, compared with the results based on MHD simulation, the effect of pressure anisotropy in our hybrid simulation is less obvious, which may be caused by the different conditions used in different simulation modes.