Abstract: To address the multi-parameter coupling problem in conventional ion line parameter inversion of incoherent scatter radar (ISR), this study explores a new method for high-precision parameter extraction by exploiting the fine structure of the secondary splitting of the high-frequency plasma lines. Leveraging the favorable observational geometric of the Sanya Incoherent Scatter Radar (SYISR), a numerical forward model of full the incoherent scatter spectrum under magnetized and collisional conditions is constructed based on Kudeki's generalized theoretical framework. Simulation results demonstrate that when the angle between the radar line of sight and the direction perpendicular to the geomagnetic field decreases to a specific range (e.g., 20^○), the plasma line exhibits a pronounced secondary splitting phenomenon near twice the electron gyrofrequency. Quantitative analysis reveals that the frequency separation of the split double peaks increases with rising electron temperature. At low temperature (T_e ≤ 2000 K), the splitting width agrees well with the theoretical approximate formula; however, at elevated temperatures (T_e > 2000 K), the truncation error of the approximation grows substantially. These findings indicate that simple approximate formulas are insufficient for inverting ionospheric parameters in high-temperature regimes, and that full-spectrum numerical forward modeling incorporating the complete physical mechanisms is essential for achieving high-precision electron temperature retrieval. The results provide a theoretical foundation for SYISR’s dedicated plasma line observations and high-precision data processing.