Due to the closed environment during deep hole boring, it is impossible to observe the working state of the boring bar. Studies show that monitoring the cutting force is the most direct and effective way to reflect the processing status. In this regard, a cutting force monitoring system is designed in the present study for the boring process. The main idea of the designed monitoring system is the piezoelectric effect of the strain gauge. When the tool tip is subjected to the cutting force, the sensor deforms and the strain sensor generates a voltage signal. Accordingly, the cutting force can be obtained by establishing the correlation between the voltage and the applied cutting force. The force of the boring bar and the output of the sensor were analyzed, and an experimental platform for monitoring the boring force was built. This method is applied in a case study and the obtained results demonstrate that the developed cutting force monitoring system has good compatibility, high precision and good dynamic characteristics. It is found that that the measurement error of the designed system in the boring process is less than 9.18%, which meets the accuracy requirements of measurements in the dynamic cutting force under machining conditions.