Micro leakage detection of subsea gas pipelines is crucial for the safety of marine engineering. Acoustic imaging instruments are an important means of detecting micro leaks in underwater gas pipelines. However, traditional techniques have insufficient detection accuracy in complex shallow water environments, making it difficult to identify micro leaks early. Therefore, this article designs a high-precision underwater acoustic imaging instrument based on multi beam forward-looking acoustic imaging technology. By utilizing the statistical differences between echo and reverberation, echo and noise in the echo domain, the separation of echo and interference signals is achieved, and the intensity characteristics of pipelines and leakage areas are obtained from the echo domain. This instrument can use the fusion processing of echo domain and image domain to detect micro leaks, and estimate the leakage amount based on the degree of bubbles and leakage speed. The experimental results show that the designed and developed acoustic imaging instrument can determine the density of bubbles, detect micro leaks of bubbles, and locate the location of micro leaks. For situations where there is a jet state, the pressure is 3 MPa, the leakage aperture is 0.5 mm, and the micro leakage amount is much less than 0.5%, this instrument can perform clear detection at a distance of 10 m. It has great potential applications in the field of micro leak detection in submarine pipelines and underwater production systems.