Abstract:W51M (W51 Main) is a massive star-forming region associated with the H$_II$ region, in which numerous molecular lines, H and He recombination lines can be detected. Study of these lines is helpful to understand the properties and physical environment of W51M. Based on the observation data of the Tianma 65-meter telescope, owned by Shanghai Astronomical Observatory, Chinese Academy of Sciences, the H and He recombination lines of the main quantum number between 74 and 117 were detected. Combined with their Doppler broadening, the electron temperature of the nebula was calculated. It was found that the electron temperature of the H$_II$ region was about 7400K, and the He+/H+ ionic abundance ratio was about 0.09, which was basically consistent with previous results. Considering the high signal-to-noise ratio of those recombination lines, i.e. H$(n) \alpha(74\leqslant n \leqslant 78)$, the calculated average turbulent velocity of W51M is 13.767kmcdots-1. This work discusses the identification of recombination lines in W51M or other H$_II$ regions, and the acquisition of electron temperature, turbulent velocity, and other physical parameters, such as electron number density, the element abundance, and star formation rate. So it is of positive significance for future study.