The modern natural law concept provides value guidance for the construction of legal system of ecological benefits. Ecological welfare, to meet the needs of the residents' survival and development, is provided by the government in the form of public service focusing on the social ecological benefits. Starting with balancing the ecological interests, the legal system means to realize the ultimate goal of sharing the ecological welfare. The legal system of ecological welfare corresponds with the concept of the modern natural law on the value's starting point, mediation and target dimension. The construction of the legal ecological welfare system should follow the guidance of the "rational concept", "human equity", and the "social contract", which come from the modern natural law, and respect reason. Based on the collective sharing of human rights, it is meant to realize the fair sharing of ecological welfare, and the distribution should stay under the supervising of the government.