The invention provides a landform measuring instrument for a seabed foundation of an ocean platform. The landform measuring instrument mainly comprises an underwater extension set, an overwater extension set, and a cable for connecting the underwater extension set with the overwater extension set, wherein the underwater extension set is used for transmitting a high-frequency acoustic signal into water, the acoustic wave reaches the seabed foundation of the platform and then is reflected by the seabed foundation of the platform, the reflected signal is received by the underwater extension set again and subjected to conditioning operations such as filtering and amplifying, and then the processed signal is transmitted to the overwater extension set by the cable to be processed so as to obtain 255 depth measurement values. The landform measuring instrument is designed based on the multi-beam acoustic detection basic principle; and the wide coverage of the ultrasonic wave in detection can be realized by a multi-channel transmitting transducer array, and the seabed scattered echo signals can be received with high resolution by a multi-channel receiving transducer array, so that the seabed foundation of the ocean platform can be effectively measured with high precision and high efficiency.