Crank angle between extreme positions and transmission angle are two important parameters. Equation which research relation between γ

min

and θ is set up by utilizing supplementary angle β. β* is calculated while γ

min

equals maximum by utilizing procedure of Matlab

and the relation between γ

min

and θ is elaborated in detail. Rotating center position of crank is determined by β*

so as to assure the best trasmission performances in crank-slid mechanism.