Avalanche photo diodes (APDs) are parallel connected in multi pixel photon counter (MPPC). The output pulse is distorted when photon arrival time gets closer, and discrete photon arrival time is unable to resolve. With photon distribution and output pulse considered, analytical form of discrete photon arrival time detected in laser ranging is derived with deconvolution from the output pulse. Also, ranging data size is increased, helpful for the recognition of efficient photons from noise. In the algorithm, single pulse response is approximated to Gaussian form, and effects of time jitter on photon discrimination are studied. Consumed the time jitter of pulse response is 50~250 ps, both statistical distribution histogram and the relation of peak-valley contrast, time interval and time jitter are obtained with three photons. Data sizes before and after deconvolution are compared in kHz laser ranging system during 1 s observation time. Results show discrete time is able to be resolved when peak-valley contrast is above 10 in histogram, and the discrimination time resolution is 0.2~0.7 ns.