In bi-prediction of merge/skip and advanced motion vector prediction(AMVP) modes, current block is predicted by averaging two uni-reference blocks. In this paper, statistical experiments show that averaged bi-prediction is not a good choice for merge/skip mode, compared with AMVP mode. And we propose an adaptive weighted bi-prediction method for merge/skip mode according to the similarities between current block and its two uni-predictors. The uni-predictor, which is more similar to current block, would be assigned with larger weighting factor. As pixel values of current block are unknown in decoder before conducting motion compensation, the similarity between current block and uni-reference block is estimated by similarity between their corresponding spatial neighboring pixels. The results show that the proposed method achieves 0.55% BD reduction on average over the reference software JEM 6.0.