Abstract: The technology of pulsed hydraulic fracluring is an important means to transform low permeability reservoir, through the double action of water wedge effect and pulse fatigue damage, the fracture network is communicated to improve the conductivity of low permeability reservoir. In the laboratory test of pulsating hydraulic fracturing, the sealing problem of prefabricated hole in the sample is the key to determine the success of hydraulic fracturing test. The initiation pressure is also an important index to evaluate the sealing effect of pulse sealing section. In this paper, the relationship of the mechanical properties between the weak joint surface of the sealing section and coal rock is established, and the influence of different frequencies on the initiation pressure of coal rock is established, and the influence of different frequencies on the initiation pressure of coal rock is studied. Finally, based on the initiation pressure, the fitting of the damage value of initiation pressure obtained that empirical formula of prefabricated hole sealing pressure, gived a basis for sealing of pulse hydraulic fracturing.