Abstract: The length of hydraulic jump in the gradually broadened channels is studied in this paper. Firstly,the hydraulic pressure acting on the hydraulic jump in the gradually broadened channel is analyzed,and why the length of hydraulic jump is always shorter in the gradually broadened channel than in the non-broadened channel expounded Considering the influence of the divergence angles on the jump,an approximate expression for the water surface profile of the jump in the gradually broad ened channel is written based on this analysis From the expression,the momentum equation and the cont inuous equation of the flow,the semi empirical formula for calculating the length of the jump in the gradually broadened channel is derived At the same time,the simplified solution to the semi empirical formula is proposed by employing an empirical formula for calculating the length of hydraulic jump in the non broadened channel Secondly,the limitations of the semi empirical formula are pointed out Based on the limitations,the applicable ranges of the semi empirical formula are obtained In the ranges the validity of the semi empirical formula is verified with the experimental data Lastly,the most empirical formulae for calculating the length of hydraulic jump in the gradually broadened channel are classified and some are recommended for the designers of the stilling basin We hope that the recommendation is useful to the designers.