The invention discloses a cable tray automatic positioning device for power supply. The cable tray automatic positioning device comprises a first fixing part, a second fixing part, a pushing device, aclamping device and a positioning device; the second fixing part is arranged above the first fixing part, and slidably connected with the first fixing part; a cable tray is placed at the top of the second fixing part, and cable reels are arranged at the two ends of the cable tray; the clamping device comprises a first motor, a first two-way threaded rod, a first moving part limiting part and a clamping assembly; the pushing device comprises a third motor, a third moving part, a threaded rod and a pushing plate; and the positioning device comprises a first fixing plate, a second fixing plate,a second motor, a second two-way threaded rod and a second moving part. According to the cable tray automatic positioning device for power supply, operation is simple and convenient, the clamping effect and the positioning effect are excellent, the cable tray can be firmly fixed, the cable tray is prevented from loosening and bringing hidden safety hazards, and placement of the cable tray can be more neatly.