Abstract: In the ionospheric monitoring, one of the key techniques is the Incoherent scatter radar (ISR), which usually uses the so called ion line spectra resulted from the ion acoustic wave to derive multiple plasma parameters including electron density, electron and ion temperature, and ion velocity and composition. In addition to the ion line, ISR could also measure the so called plasma line spectra due to the existence of Langmuir wave, the dispersion relation of which is associated with the electron density and temperature. In the conventional ion line inversions, the temperature–ion composition ambiguity (TICA) and the systematic bias hinder the accuracy of retrieved parameters. To address these issues, here we propose an improved method through incorporating the information of plasma line into the ion line fitting process. We expect that the retrieval accuracy could be enhanced with the independent constraint on electron density and electron temperature obtained from the plasma line. Simulations based on the International Reference Ionosphere demonstrate that the combined ion line–plasma line method significantly reduces deviations in electron density and temperature，and it can improve the impact of the TICA effect to a certain extent. The comparison of the experimental results of Sanya Incoherent Scatter Radar with the ionosonde data on June 6, 2022 shows that this method has a certain effect on improving the electron density. This study establishes the feasibility of combined inversion for ISR data analysis, enabling more accurate and calibration-free ionospheric parameter retrievals in the future.