Abstract: As the important parameters in designing the stilling basin, calculation of the length of the free hydraulic jump plays a major role in the safety, stability and economization for the stilling basin. The research on the variation laws of the vortex roll length of the free hydraulic jump and the hydraulic jump length occurred on the uniform rough height bed of the stilling basin was carried out according to establishing the motion equations for water body particle in the hydraulic jump zone, and developing a theoretical method for calculation of the vortex roll length of the free hydraulic jump and the hydraulic jump length, and the physical parameters are calibrated by the given expressions based on the testing data from the existing literatures. Research results show that both of the hydraulic jump vortex roll length and the hydraulic jump length on the uniform rough height bed of the stilling basin increase with the increase of the upstream Froude number, upstream supercritical water depth and the conjugate depth ratio, and at the same time decrease with the increase of the equivalent roughness of the riverbed. From the verification results it is found that the calculated values are well approximate to the measured values of the hydraulic jump vortex roll length and the hydraulic jump lengths.