Avalanche photon diode and avalanche diode array, working in Geiger mode, have single photon detection capability. The structure of guard ring is the key factor to avoid the premature edge breakdown of the avalanche diode and increase the maximum bias voltage. A new structure of the guard ring is proposed in this letter, in which the floating guard ring is put outside the p-well guard ring. Simulation results indicate that the maximum bias voltage of the proposed guard ring is higher than that of the state-of-the-art methods.