The invention discloses an acoustic-optic fused coral activity detection system and an acoustic-optic fused coral activity detection method. According to hardening and whitening reflected by whiteningfeature of coral, an accurate position and hardness degree of a target coral are inverted through ultrasonic echo, colors of the coral are acquired through auxiliary optical measures, fusion treatment is executed for ultrasonic data and optic data acquired for the corals at different sea area environment, and consequently, activity of the corals is judged. The system comprises a front-end acquisition device for acquiring the ultrasonic data and the optic data and a background terminal which takes charge of processing and displaying the acquired data and realizing man-machine interaction. Theinvention provides an all-weather, low-cost and light-weight intelligent solution; economic and time cost of detection works is reduced, limit of ocean light conditions to the conventional optic methods is broken; and robustness and accuracy of a detection result are improved