The invention discloses a groove-gate type gate-drain composite field plate transistor with high electron mobility. The transistor comprises, from bottom to top, a substrate (1), a transition layer (2), a barrier layer (3), a source electrode (4), a drain electrode (5), a groove gate (7), a passivation layer (8), a gate field plate (9), a drain field plate (11) and a protection layer (12); the drain field plate (11) is electrically connected with the drain electrode (5), the groove gate (7) is electrically connected with the gate field plate (9), wherein, a groove (6) is opened on the barrier layer (3); and n floating field plates (10) are deposited on the passivation layer arranged between the gate field plate and the drain field plate. All the floating field plates have the same size and are in a floating state, and the floating field plates are equidistantly distributed between the gate field plate and the drain field plate. The n floating plates, the gate field plate and the drain plate are completed on the passivation layer by one-time process. The transistor has the advantages of simple process, good reliability and high breakdown voltage, and can be used for fabricating high power devices based on a wide band gap compound semiconductor material heterojunction.