Recently the direct TOF Lidar receivers employ cell averaging constant false alarm rate (CA-CFAR) technique to determine the threshold for the reflected pulses. CA-CFAR locally estimates the mean level of the noise from a predefined interval. The length of this interval is determined by a fixed number of reference cells. CA-CFAR with small number of reference cells fails to detect long distance objects. Conversely, setting reference cells to a large number can’t resolve closely spaced objects even at short distances. This paper presents an adaptive CA-CFAR adaptively determining the optimal number of reference cells. Simulation results show the capability of the proposed method to do both detecting long distance objects and resolving closely spaced objects at short distances.