The chief task of environmental quality evaluation is to give weight. Facing the current situation o f environmental quality evaluation, we combine principle components to linear programming techniques and make the model called PC - LP based on every factor’s environmental monitoring date of every site in the city. Its main contents are: to determine betteror worst consequence through the model of PC, then to determine environmental quality evaluation’s weight through the model of LP. The result is more accurate and scientific, a case study is presented in this paper.