Abstract: By adding a binary relation and a number of assessment factors into an approximation space,a rough assessment system was obtained．Based on the assessment factors,the concepts of the weight and the comprehensive weight were defined,which leaded to the comprehensive lower value of an edge set．So,a path could be optimized by making use of the comprehensive lower value,also an algorithm called path optimization algorithm was formed．Moreover,by a rough assessment system which describes supply relationships between enterprises,a mathematical model of practical problems was constructed．Supply paths were therefore optimized,which resulted in applying path optimization algorithm to the supply paths．This demonstrates the validity of the algorithm.

Key words: Rough assessment system,Assessment factor,Weight,Comprehensive lower value,Path optimization algorithm