In response to the problems in offshore oilfield injection wells, such as the reduction of injection volume due to pollution, the shortening of the effective period of acidizing for injection enhancement, and the low injection pressure of injection pumps, a pulsed high-pressure dilation and injection enhancement technology based on rock fatigue damage was proposed by organically combining rock expansion and high-pressure water injection, and the technical feasibility study and application were carried out. By using the principle of rock dilation, pulsed high-pressure water injection was carried out, which makes the internal crystals of reservoir rocks produce two micro-fracture states, namely tensile fractures and shear fractures, through the two effects of shear slip and pressure expansion. Through the true triaxial rock mechanics and CT scanning experiments based on rock fatigue damage, the micro-fracture propagation mechanism under the action of pulsed high-pressure dilation was revealed. The application in two difficult wells on site shows that the apparent water absorption index has increased by 3.25 times and 2.54 times respectively, and the effective period of the measure has been extended by at least 335%. This injection enhancement technology has the advantages of low cost without moving the pipe string, no change to the existing water injection facilities on offshore platforms, large treatment radius, and long effective period. It can provide a new direction for the optimization of injection enhancement technologies for injection wells in domestic and foreign oilfields.