Abstract: The online monitoring technology of oil and gas pipeline wall thickness based on ultrasonic testing technology is of great significance in reducing human monitoring costs and improving the early warning ability of oil and gas pipeline thinning and failure. A high-precision ultrasonic pipeline wall thickness online monitoring system with multiple channels was designed based on the ultrasonic reflection method. Multiple wall thickness online monitoring experiments were conducted at different test temperatures, and the results were analyzed and corrected to obtain the correction equation and model. The experimental results showed that the proposed data fitting correction scheme achieved an absolute error of ±0.04 mm and a relative error of 1% for ultrasonic thickness measurement of pipeline wall thickness, achieving high-precision monitoring of oil and gas pipeline wall thickness.