The determination of the width of the regulation line in the channel regulation is one of the key factors for the success or failure of regulation. In this paper，the calculation formula of the regulation width is improved on the basis of considering the stability of the navigation channel and the capacity of ships ascending rapids. Also，a formula for calculating the regulation width of the sand-pebble shoal in mountainous rivers is put forward. A mathematical model is established to verify and optimize the regulation width calculated by the formula in this paper through an engineering example. The calculation of regulation width is systematic work，the regulation widths calculated by the traditional formula，and the formula in this paper can only be used as reference values. To achieve a good regulation effect，the regulation width needs to be further modified by the mathematical model and physical model experiment.