The invention discloses a method for detecting primary frequency modulation capacity of power system units. The method includes: using WAMS (wide area measurement system) time sequence real-time library data to detect whether a primary frequency modulation event occurs or not; using the WAMS time sequence real-time library data to count unit operation time and design a visualized man-machine interface. By the method, the problem that a scheduling center cannot learn about the primary frequency modulation capacity of each unit in real time when power grid frequency is abnormal is solved. The fast and efficiency method is provided for power grid scheduling operators to detect the primary frequency modulation capacity, monitor the primary frequency modulation capacity of the units in real time, and increased the primary frequency modulation capacity of the units.