Under the conditions of giving the length of the rocker CD,swinging angle φ and advance-to return-time ratio K（extreme position angle θ）,in order to design crank-rocker mechanism with the maximum value of minimum transmission angle γmin,the supplementary angle β（be used to determine the position angle of the rotation center A of crank） is introduced,the function relation of minimum transmission angle γminand the supplementary angle β is established.Then the maximum value of minimum transmission angle γmincan be obtained by utilizing procedure of Matlab.At the same time,in view of the different K value,the mechanism of type selection is classified.Then,points out the typeⅠ and Ⅱmechanism can be used to design and typeⅠ mechanism is better in force-passing property when K ∈（1,3）.When K∈[3,+ ∞),if type Ⅱ mechanism is used to carry on the design,which will not be able to meet the requirement of the rocker swinging angle,if typeⅠ mechanism is used,which has low efficiency and is not conductive to transmission of the mechanism.