A residual liquid inspection system based on double infrared sensors and AT89S52 was designed to resolve the low speed and accuracy problems. The fundamental of the system is that it takes different time for infrared to pass different media with the same distance. The hardware configuration, the software design flow, and the measurement process of the system were introduced. Experimental results showed that the system has the features of convenient and high accuracy; the accuracy is 99% while it is used in the beer filling line of 72,000 bottles per hour. It has practical application value.