Line commutated converter high voltage direct current (LCC-HVDC) transmission has unique advantages and plays an irreplaceable role in the power system. It is of great significance to study the commutation process. The traditional ideal model of commutation process neglects many valve parameters. In this paper, the consistency problems of valve parameters and early slight faults of converter station are considered. The commutation process is studied and a more accurate module is built, which revises the traditional ideal commutation model. Based on the parameters of Haminan-Zhengzhou HVDC transmission project, the analysis results of the theoretical model are given. The results show that the consistency of valve parameters and the early slight fault of valve bridge arm have obvious influence on LCC-HVDC commutation process and stable operation. Finally, this model is verified by Matlab/Simulink simulation. Based on the model proposed, the control angle of the inverter valve can be calculated and controlled more accurately. Besides, the reactive power demand can be optimized and the commutation failure can be mitigated. What's more, the slight fault and aging of the valves can also be detected by monitoring of the commutation process. The paper aims to provide theoretical support for the economical and reliable operation of LCC-HVDC transmission.