The invention discloses a front mixing chirp modulation photon counting laser radar, belonging to the technical field of counting laser radars. The radar solves the problems that the inherent dead time of a Gm-APD device adopted by the existing chirp modulation photon counting laser radar limits the frequency of sampling detection and then restricts the ranging accuracy. The radar comprises a signal transmitter, a laser, a transmitting optical system, an adjustable gate width control module, a receiving optical system, a Gm-APD single photon detector, a low-pass filter, a Fourier transform module and a computer; a Gm-APD sampling gate is directly modulated by using local oscillator modulation signals, so that the width of the sampling gate is directly proportional to the intensity of the local oscillator modulation signals; and the local oscillator modulation signals are mixed with echo reflection signals through time changes of the sampling gate, so that Gm-APD responds to mixed intermediate frequency signals. The front mixing chirp modulation photon counting laser radar serves as a counting laser radar.