The invention discloses an underwater multi-channel hydraulic fast connecting device. According to the structure of a fixed end assembly, a big horn mouth of a shell is provided with an installing joint along a flange, a plurality of hydraulic joints A are installed on a bottom plate of the big horn mouth of the shell, a locking sleeve is fixedly arranged at the axis position of the bottom plate of the shell downward, the head portion of the locking sleeve is provided with a tooth groove, a plurality of positioning sliding grooves are formed in the outer circumference of the locking sleeve, and guiding keys are arranged at the inner wall of the shell; according to the structure of a movable end assembly, the movable end assembly comprises a guiding cylinder of a hollow structure, the upper port of the guiding cylinder is a small horn mouth, the upper section of the guiding cylinder is a disc-shaped guiding cylinder panel, a plurality of positioning pins are arranged radially on the upper surface, exceeding the guiding cylinder panel, of the guiding cylinder, a plurality of hydraulic joints B are located uniformly along the circumference of the guiding cylinder panel, a locking shaft is arranged in the cylinder body of the guiding cylinder in a sleeved mode, and a lower port flange of the guiding cylinder, a limiting head and an ROV end socket are fixedly connected. The underwater multi-channel hydraulic fast connecting device has the advantages of being simple in operation and high in reliability.