NaI (TI) detector is a typical scintillator radiation detector, and its detection process involves radiation energy deposition, generation and transport of visible light signal, photoelectric conversion, signal processing and other physical processes. Firstly, the process of ray particles converting into visible light signal output in crystals was simulated and analyzed by Monte Carlo method, Birks formula and ray tracing program. Combined with the index parameters of photomultiplier tube and signal processing circuit, the pulse voltage signal parameters for the final output of the detector were obtained. Then, the experiment was verified by using Φ50 mm×50 mm NaI (TI) crystal-coupled photomultiplier in ¹³⁷Cs source radiation field. The experimental results show that the rise/fall time ratio of the output pulse signal of detector is 0.39, which is about 7.69% different than the simulated value of 0.36, indicating that the output results of the simulation calculation model are basically consistent with the measured data, which preliminarily proves the correctness of the simulation calculation model and calculation analysis process. The proposed method is of certain reference significance for deeply understanding transmission law of fluorescent visible light excited by radiation particles in crystal scintillator and optimization design of scintillator radiation detector system.