In view of the shortcomings of the lathe tool measuring instrument used in the present experimental teaching, a device for measuring the geometric angle of the lathe tool by using magnetic encoder is studied. The device combines the machine and electricity organically to realize the digital display of the measuring instrument. At the same time, in consideration of the geometric angle measurement of the lathe tool completed in the reference plane, we design the mechanical structure of the measuring instrument and the 3 ways of realizing measure slice, shaft shoulder and shaft end. The instrument is simple in structure and convenient in measurement. It can measure the geometric angle of the lathe tool and improve the measurement accuracy. It is applied to the experimental teaching of the undergraduate course and has achieved very good teaching effect.