Based on the forming mechanism of cumulative environment effect of compound ecosystem on development, and according to the nonlinear dynamic character of system and environmental effect-response process curve, the time-series multivariable decision-making mode was preferred. Owing to the weighting information came from objective environment and the greater the damage contribution to ecosystem, the higher the weighting value, at the same time, the environmental effect takes a kind of linear, serious sharpening trend and leave smoothing character. So in the paper based on the principle of ‘loss-density curve' advanced by L. D. James, the relative importance weighting of water environment factor and exponent character a quantitative calibrating scale model on of dynamic monitoring factor of environmental effect was set up in light of factors threshold value. In the decision-making theoretical model time and space parameter is taken into account so for the decision-making process and results they also indicated the time series character. To any compound ecosystem, the preferred method possessed a certain directing for the system regulation and dynamic appraise with long-term or period ambiguity character. In the paper it was proved reasonable by means of theoretical analysis. In the other relative paper referenced of author, the dynamic decision-making model had been proved effective. However owing to the limitation of paper length only the factor weighting method on compound ecosystem with S curve trend was explained more detailed. In addition a great many long-term ecological factors was required to conform the threshold curve coefficient so in the paper the application example is not given.