Abstract: In this paper, B.B, Golubef method^[1] is used for calculating the radial diffuse flow between two parallel disks for the first step, the momentum integral equation together with the energy integral equation is derived from the boundary layer momentum equation,then the expression of secondary approximation explicit function which is the entrance region duct length accompanied by the boundary layer thickness can be obtained by using Picard iteration^[2] in the solution of the energy integral equatio,.Therefore, this has made it possible to analyze directly and analytically the coefficients of entrance region effect, Especially when the outer diameter of the disk is less than the entrance region length, the advantage of this method can be prominently shown.Because energy integral equation was employed, the terms in the pressure loss coefficient can only be independently derived theoretically.The computable value of the pressure loss coefficient presented in this paper is nearer to the testing value than ref.[3] when the entrance correction Reynolds number Re<100.Therefore, the results in this paper within Re<100 are both reliable and simple.