Abstract: This paper deals mainly with laws of velocity distribution and the characters of secondary vector, Reynolds stress and intensity of velocity fluctuation in three dimensional flow to verify authors' theory. According id the partition method of hydraulic radius,the velocity profile normal of the boundary can be described by Prandtl - Karman formula if the friction velocities in formula are replaced with the location and overall friction velocities respectively determined by author's method.Tracy's experimental data in a smooth rectangular duct is in good agreement with the formulas presented in this paper. This paper also describes the area and shape of secondary vetor and explains the reason of deflection of maximum velocity near axis in conner region and presents formulas to describe the intensity of velocity fluctuation.