How to apply the Lagrange equation to the continuous medium mechanics has been a theoretical issue of academic circles. Using variational derivative concepts and operational rules, the properties of variational derivative in Lagrange equation are studied. The Lagrange equation is applied to linear elastic dynamics and nonlinear elastic dynamics, and some corresponding numerical examples are given. The result shows that it is a feasible way to solve the problem of the application of Lagrange equation to the mechanics of continuous media by using the variational integral calculus.