Artificial anal sphincter has gradually become an emerging means of treating anal incontinence. However, most of the systems cannot be implanted in the human body for a long time due to insufficient reliability. Therefore, this paper has designed and improved a novel bionic artificial anal sphincter (BAAS). In order to make it work reliably for a long time, we first optimized and improved key parts to increase their strength. Given the humid working environment in the body, we optimized the design of the waterproof pressure sensor and carried out experimental research on the sealing of the circuit board and the overall sealing. When evaluating the improved system, I used simulation to analyze the structural strength and motion characteristics of the BAAS and used underwater experiments to simulate the human environment to evaluate the waterproofness of the system. The results showed that the strength of the key joint increased by 49.4%, the average clamping time and opening time of the prosthesis were 14.5 s and 13.4 s, respectively, and the angular velocity of the pendulum rod approaching the intestine was about 4.5 deg/s, which was in line with the normal defecation process of the human body. The performance is stable and reliable in the 20-day underwater body fluid simulation experiment. BAAS basically meets the application needs of long-term implantation in the treatment of fecal incontinence.