The invention discloses a control method of a thermal generator set in response to power grid low-frequency fault adjustment. When in response to the low-frequency fault of a power grid, the primary frequency adjustment function of the thermal generator set is greatly influenced. The control method includes acquiring a power grid frequency difference signal, determining whether the power grid frequency offset is lower than a low-frequency fault support threshold; if yes, evaluating the current low-frequency support capacity of the thermal generator set based on the frequency difference being lower than the subjection range of the low frequency fault support threshold, and rapidly cutting the extraction adjustable and extraction non-adjustable high-pressure heaters of the set by grading based on the evaluation result, and meanwhile, improving the set boiler instruction to a target value through load control means to complete the rapid response of the set under the large frequency difference of the power grid; and if no, performing primary frequency modulation of the set in a normal mode. The control method not only influences the function of the normal primary frequency modulation of the set, and can rapidly, stably, and enduringly provide power support when the power grid has low-frequency faults.