Abstract: In this paper,some numerical experiments of adjoint,ariational assimilation has been performed using the famous Lorenz model.With the increase of medel sensitivity to initial condition,finding the initial values which harmonize with the Lorenzmodel become more and more difficult until the scheme is failure on some situation.This shows that the four-dimensional assimilation have some relation with predictability.On the other hand,with the increase of errors in the Lorenz model,the effects of variational assimilation become worse and worse until the forcasting has no meaning.If we perform variational assimilation and retrieve the model parameters at the same time,The consequene of forcasting can improve greatly based on Lorenz model.