The invention discloses a fluid-driven impactor, a power transmission mechanism for the impactor and the use of the impactor. In the prior art, the working life of the impactor is short, since a rubber primary seal and an upper fluid-diverging lid for the fluid-driven impactor are both liable to erosion and the efficiency in transmitting power is low due to the complexity of the power transmission mechanism. In order to increase the drilling speed and/or extend the life of the impactor, the side cavity passage is formed in such a way that the inner wall of the outer pipe is isolated from the side cavity passage in a watertight manner without the use of the rubber primary seal. The loss in transmitting power is minimized by integrating the anvil of the power transmission mechanism and the lower joint. The problem of abrasion of the fluid-diverging hole is overcome and the nozzle can be used with different fluid flow by mounting a replaceable nozzle in the upper fluid-diverging lid, the nozzle selected from a series of nozzles with various inner diameters and made of a material more wearable than the material for diverging lid the upper fluid.