A single photon avalanche diode with non-contact guard ring was proposed based on standard CMOS technology. The influences of the guard ring's spacing on the electric field distribution and the avalanche probability of the device were analyzed by using Silvaco Atlas. The dark count probability and the photon detection efficiency of SPAD operated under gate-model were calculated based on a physical model. The results shown that the device has optimal performance at the spacing d=0.6 μm. Under these conditions, a breakdown voltage of 13.5 V is obtained, and the dark current is as low as 10－11A. When the excess bias voltage is 2.5 V, the dark count probability is only 0.38%, the responsivities within the spectral range wavelength of 400 nm to 700 nm are decent, and the peak photon detection efficiency is up to 39% at 500 nm.