The invention discloses a computer dynamic simulation method of determining a true strain effect of a seawater aggregate concrete. A disconnect-type Hopkinson compression bar test and a corresponding finite element analytical model of the seawater aggregate concrete are utilized. The method comprises the steps of using a measured compression bar incident wave as an input stress wave of the finite element model; selecting and using an extended Drucker-Prager model as a material model of the seawater congregate concrete basal body, wherein the strain rate effect is not set, and only simulating the increase of the strength of the seawater congregate concrete caused by a sidewise inertial confinement effect under a high strain rate; determining the true strain rate effect of the seawater congregate concrete according to the strain rate effect obtained through compression bar test and the strain rate effect caused by the sidewise inertial and end face friction. According to the computer dynamic simulation method of determining the true strain effect of the seawater aggregate concrete, the situation that a complicatedly designed test decouples the true strain rate effect of the seawater congregate concrete with a structure of an inner shell body and the strain rate effect caused by the sidewise restraint is avoided, the result is quick and accurate, and the computer dynamic simulation method of determining the true strain effect of the seawater aggregate concrete has better practical value.