To meet the needs of designing four-bar mechanism and enrich the theory in design, this paper expands the method of designing four-bar mechanism by illustrating, and also presents some new methods and the whole process of each designing method on condition that the length of one of the three components ( i.e. rocking lever, crank and link) in the crank-rocker mechanism, the length of the mechanism frame and the angle of the rocking lever are given. The methods are of some value in theory and practice.