Research conclusions：(1)Impact on switch rail is decreasing when the train passing through the turnout on the adverse route and the straightway length of switch rail is increasing with the increasing of disjoint value．Increasing the disjoint value can improve the service life of switch rail．(2)Increasing the half cut surface appropriately will shorten the length of turnout and increase the straightway length of switch rail．(3)The disjoint value is reasonable when the offset of half cut surface is equal to the maximum clearance of wheel-set under the condition of basic parameters of turnout are fixed． (4)The reasonable disjoint values are 16 mm and 23 mm when the basic parameters are consistent with current No． 28．3 m long turnout．which front lengths of basic rail are 2．620 m and 2．020 m．(5)This paper studies has some reference significance to the structure design of the No．9 turnout．