There are widespread problems with high injection pressure and low water injection in the process of water injection development in offshore oilfields. The conventional acidification measures are short-lived and have high operating costs, which seriously affects oilfield development. High-pressure dilation technology can improve the injection rate and extend the effective period of injection. The representative unconsolidated sand core samples were taken from the offshore oilfield for rock mechanics tests, dilation laboratory simulation experiments and numerical simulations, to study the dilation mechanism and main controlling factors of unconsolidated sandstone in offshore oilfields, and the dilation technology has been applied in offshore oilfields. It is shown that the dilation angles of unconsolidated sand in offshore oilfields are much larger than those of the Athabasca oil sand in Canada, which has the basic conditions for applying dilation technology. It is conducive to the development of complex shear and tensile areas with a slow injection rate, but a high injection rate tends to form a single crack. It is beneficial to generate complex.