In the process of precision cutting machining, in order to obtain smooth surface, the tool wear is an important factor besides the optimizing the cutting parameters. When the tool was worn to a certain degree, the machined surface quality would be very difference after cutting with the tool wear. So in the process of precision cutting, the measuring of the tool wear is a very important problem. In the paper, A simple and reliable monitoring method based on laser-CCD trigonometric measurement is proposed for tool wear sensing on-line in the automation of precision cutting processes. With laser-CCD trigonometric measurement, the tool wear is measured. When the tool wear is to a certain degree, the measurement system give the alarm and the tool must be replaced, and then go on to cut work-pieces with new tool. Much experimental studies of the precision cutting are carried out with the measuring system and the experimental result is given. The results show that the measurement accuracy of the measurement system is +/- 0.1 micrometers , it can be used very well in the on-line measurement and workplace's surface quality is guaranteed.