Abstract: The energy dissipation and scour prevention in the downstream of the release structures is one of the important measures to ensure the safety of hydroprojects. The abruptly expanding hydraulic jump is one of the forms of the energy dissipation of the hydraulic jump, which is widely applied to the practical hydraulic engineering. Some studies of the equations for the abruptly expanding hydraulic jump and its hydraulic characteristics including the average water depth in the backflow zone are carried out in this research. An empirical formula of coefficient α is suggested based on the assumption of the average depth h₃²=α(h₁²+h₂²) in the backflow zone, and the equation of the abruptly expanding hydraulic jump is derived by the momentum conservation theory, and the explicit solution of the abruptly expanding hydraulic jump is given. The experimental results show that the average error between the explicit solution of the abruptly expanding hydraulic jump equation and the experimental data is 5.481%. Of 90 groups of the experimental data, there are 57 groups with the errors between the explicit solution of the abruptly expanding hydraulic jump equation and the experimental data being less than 5%. Obviously, the explicit solutions of the equation in this paper for the abruptly expanding hydraulic jump are in good agreement with the experimental data. It is proved that the equation in this paper for the explicit solution of the abruptly expanding hydraulic jump is reliable, practical and accurate, and can be applied to solving practical engineering problems.