In visualization field, Focus+Context techniques have been developed to visualize large, complex models on the display device with limited resolution. In this work, we propose a novel method for Focus+Context visualization based on optimal mass transportation. An optimal mass transportation map deforms a volume to itself, transforms the source measure (volumetric element) to the target measure with the minimal transportation cost. Solving the optimal mass transportation problem is equivalent to a convex optimization, and can be converted to computing power Voronoi diagrams in classical computational geometry. Comparing to existing approaches, the proposed method has solid theoretic foundation, which guarantees the existence, uniqueness and the smoothness of the solution. It allows the user to accurately control the target measure, and select multiple focus regions with irregular shapes. The resulting deformation is globally smooth and flipping free. Experiments with several volume data sets from medical applications and scientific simulations demonstrate the effectiveness and efficiency of our method.