Single-photon avalanche diodes (SPADs) have found widespread application as efficient photon detection devices in quantum communication and 3D imaging technologies. In this study, a simulation program with an integrated circuit emphasis (SPICE) model was established for SPAD within the Cadence environment. Employing the Verilog-A language, a combination of two exponential functions was utilized to continuously describe the dynamic variation in the equivalent resistance of the SPAD in the Geiger mode region. These two exponential functions encompass the equivalent resistance characteristics of the high- and low-resistance regions, addressing the issue of non-convergence in the segmented resistance models during simulation. The SPICE model simulates the dynamic behavior of the SPAD device in the "photon reception-avalanche pulse generation-quenching-reset" operational process, as well as the static current-voltage (I-V) characteristics of SPAD from forward bias to secondary breakdown. The effectiveness and stability of this model were verified through simulations involving four quenching circuits.