Abstract: Real-time monitoring of in-core neutron flux density is crucial for reactor safety. Although self-powered neutron detectors (SPNDs) are widely used, severe core temperature fluctuations significantly alter their sensitivity. Existing studies mostly focus on single factors, lacking a systematic quantitative evaluation of the full-link cascaded physical processes. Therefore, this study proposes a full-link four-factor decomposition physical model describing the temperature dependence of SPNDs. The objective is to elucidate the decisive mechanisms of temperature variations on SPND signal responses from 300 K to 800 K, providing a theoretical basis for high-precision temperature compensation. The model decoupled the output current of the detector into a reference primary current and four independent factors: nuclear reaction rate, geometric deformation, electric field shielding, and macroscopic shunting. Based on the Monte Carlo method and the SPNDSignal platform, high-fidelity computational models containing Co, Rh, and V emitters alongside oxide insulators were constructed. The study calculated the attenuation of the nuclear reaction rate using the NJOY program, reconstructed the geometric model according to the linear expansion coefficient, simulated the space charge shielding by jointly solving the continuity and Poisson equations, and established an equivalent circuit model to analyze the shunting loss. Through step-by-step additive simulations, the independent contribution of each factor was precisely quantified. Results show that the attenuation of the nuclear reaction rate caused by neutron spectrum hardening is the absolute dominant factor leading to the signal decrease, causing a sensitivity drop of approximately (35.0±1.5)% for SPNDs. The space charge effect is a typical low-temperature threshold perturbation mechanism, but its impact is minimal under actual reactor operating conditions. When the neutron flux density is constant at 10¹³ cm⁻²·s⁻¹, when the temperature is around 300 K and the built-in negative potential barrier reaches the order of 10⁵ V does the detector sensitivity show a decrease of over 10%. As the temperature rises above 400 K, with the sudden drop in insulation resistivity, the shielding effect attenuates rapidly, and its impact falls below 1%. Supplementary simulations indicate that in practical conditions, it is difficult for the insulation layer to build up a potential barrier sufficient to significantly inhibit electron transport. Therefore, within the selected temperature range, the impact of the space charge effect on the signal output is almost negligible. Furthermore, geometric perturbations caused by thermal expansion (with a deviation of only 0.27%) and the shunting rate under extreme high-temperature conditions (in the order of 10⁻⁵) do not constitute substantial signal attenuations. In summary, the temperature response characteristics of SPNDs over a wide temperature range are determined by microscopic nuclear reaction mechanisms, and neutron spectrum hardening is the core dominant factor for sensitivity drift. The space charge effect is theoretically a severe perturbation term in the low-temperature region but can be neglected in practical engineering; similarly, geometric and shunting effects are also negligible in engineering applications.