Because the micro lenses segment the plenoptic image physically, the global optimization method is hard to be applied on the depth estimation progress and the WTA (winner-take-all) method based on the multibaseline system will generate very coarse but continuous depth map. The global optimizations method always generate robust but concrete depth map when using multi-label technique. So cost projection strategy by directly processing the lenslet plenoptic image is proposed to build the cost volume based on the projection image for global optimization. A method based on Markov Random Fields Propagation (MRFsP) is adopted by merging the modified WTA depth result to refine the concrete depth map. For validation, the depth map built with the proposed method is compared with the microlens-based optimization result, and the result shows obvious improvement.