It is very significant for reasoning dam service behavior according to the results of fusion analysis and achieving dam safety monitoring to determine the weight of multi-effect quantities. The dam multi-effect quantity evaluation system has the characteristics of randomness
and uncertainty,so measuring the uncertainty of dam system is the premise to achieve the reasons of dam service behavior accurately. The
rough degree and rough entropy are proposed to describe and measure the uncertainty of set boundary and uncertainty of knowledge respectively after using existing research results for reference based on classical rough set theory and the limitation of existing research. The improved
rough entropy model of dam system uncertainty measurement is built after combining the rough degree and rough entropy organically. Finally,
taking an engineering project for example,the aims of the weight calculation of dam multi-effect quantities and the reasonable reasoning of
dam service behavior have been realized. A new way of thinking is provided for the dam multi-effect quantities fusion analysis and evaluation.