The system based on laser transmission method to measure the plaster ointment content was introduced in this paper. The principle and structure of the system were reported in detail. The relation of the system output and the plaster ointment content was established, and this result was compared with the results by the use of commercial β-ray instrument. Both systems can detect 0.1 g variation of the ointment content, but the optoelectronic system is safer and more compact, and can be used in the plaster industry.