The invention discloses a primary frequency modulation method of a thermal power generating unit with no dead zone and automatically variable speed regulation. The primary frequency modulation capacity of a thermal power generating unit requires further improvement to fulfill the background requirements of ultra-high voltage power transmission landing, progressively increasing new energy occupation, large-scale transformation of the economic structure and the like. According to the method, an automatically sampled function is constructed for the speed regulation by eliminating a dead zone on the full frequency domain, so that part of serious work conditions in the dead zone can be screened and subjected to frequency modulation, and the speed regulation out of the dead zone is linearly changed along with frequency, and the influence of main steam pressure and temperature is concerned. According to the method, the primary frequency modulation capacity of a thermal power generating unit can be improved, the damage of a speed regulation system due to over-frequent operation cannot be caused, and the stable safety performance of the unit cannot be reduced.