We investigate the perturbation to discrete conformal invariance and the adiabatic invariants of Lagrangian systems.A variational algorithm is proposed for a system subjected to the perturbation quantities.The discrete determining equations of the perturbations to conformal invariance are established.For perturbed Lagrangian systems,the condition of the existence of adiabatic invariant is derived from the discrete perturbation to conformal invariance.The numerical simulations demonstrate that the variational algorithm has the higher precision and the longer time stability than the standard numerical method.