The algorithms to obtain sub-pixel accuracy in image matching was discussed. The resampling and surface fitting methods characteristics was analyzed. The following improvement was made to alleviate the computation burden: At first, only the model is needed to be resampled n-times; Next, (2*n-1) sub-models are generated; Again, the NCs among each sub-model and the image are calculated; At last, the maximum among the sub-model is chosen and the shifts corresponding to this sub-model are the sub-pixel displacement required. Then a new algorithm was proposed to combine the resampling and surface fitting methods. The effectiveness of the proposed algorithm was validated by the experiment.