The invention discloses an method for acquiring on-missile thin-wall inertial navigation strain, and relates to the technical field of inertial navigation system strain calculation. The method comprises the following steps of adopting an analytical method to obtain inertial navigation internal and external pressure difference so that the inertial navigation internal and external pressure difference in the missile flight process can be accurately predicted; then using the internal and external pressure difference of inertial navigation as a pressure boundary condition, and acquiring the strainvalue of an inertial navigation shell by combining transient numerical simulation based on fluid-solid coupling, so that the problems of large numerical simulation calculation error and large calculated amount of a fluid item are avoided, the accuracy and reliability of strain acquisition are ensured, and the equipment cost is low. An accurate strain value can be quickly obtained, corresponding solutions are designed for different ballistic conditions, and the method has universal applicability.