Abstract: According to the rectangular coordinate K-L, there are a great many different function expressions of OA to join the final point of a straight-line and the starting point of a circular curve. These expressions may be used for deriving a transition curve of highway. They can be a cube of parabola, an algebraic expression of sine function, 5th, 6th and nth power function of algebraic expressions. The author recommand the 5th power function of algebraic expression as a transition curve of highway after analyzing and comparing with other patterns.