Generally, the operation of the horizontally-framed miter gate in a ship lock should consider the effects of hydrodynamic resistance. If over-filling or over-emptying exists and the miter gate opens with reverse head, the hydrodynamic resistance will increase rapidly, endangering the operation safety of the miter gate. In order to study the operating characteristics of the miter gate, a prototype test is introduced in this paper. Results show that, during the filling or emptying process, when water levels at both sides of the miter gate are equal the first time, opening the gate in a timely manner can obviously avoid the influence of reverse head. Furthermore, a three-dimensional numerical model with a dynamic mesh is established for analyzing the hydrodynamic characteristics in different operating conditions. Results show that the peak value of operating load always occurs at the initial time, and the greater the submerged water depth, the larger the peak value. With the increasing of reverse head, the piston rods sustain a great compression, and the peak value appears at an early stage of gate opening. The results have a reference value for the design of a miter gate in the related engineering projects.