Laser focal plane detector is a new type of optoelectronic imaging device, which utilizes the avalanche multiplication effect of carriers inside the semiconductor to achieve high-speed, high-sensitivity, nanosecond time-resolved detection for gaze-type laser 3-D imaging system. It is mainly divided into two categories, linear and Geiger, in which the linear-mode detectors have the advantages of fast response speed, no dead time and post-pulse, and can realize single-pulse instantaneous imaging. Firstly, two architectures of linear-mode focal plane readout circuitswere introduced and their principles were briefly described in different application scenarios, then the key circuit modules of pixel units were elaborated and their advantages and disadvantages were compared, and finally two double-threshold moment identification methods to reduce walking errors were analyzed, which were intended to provide some useful references for the researchers in the related fields.