In order to upgrade the communication system from direct detection to coherent detection, an upgrade scheme is proposed by using optical coupling from space to fiber hybrid and Decision Driven Phase Locked Loop (DDPLL). The pointing error would cause coupling loss and then influence the optimal bandwidth of DDPLL. Therefore, the theoretical analysis about the optimal bandwidth of DDPLL and simulation are carried out with considering the pointing errors of transmitter and receiver. The results shows that the optimal bandwidth of DDPLL decreases with pointing errors of transmitter and receiver, and the minimum phase error increases with pointing errors of transmitter and receiver. Both of these parameters are more sensitive to the receiver pointing errors.