A system for monitoring tension forces of tendons in post-tensioning includes a hydraulic jack to apply the tension force to the tendon, a hydraulic pump to supply a hydraulic pressure to the hydraulic jack, a digital elongation length measurement sensor to measure the elongation length of the piston, a measurement unit having a data logger adapted to receive and store the elongation length data measured by the digital elongation length measurement sensor and to send the elongation length data to a main server, a digital pressure measurement sensor, and a control module adapted to receive the elongation length data from the data logger or the main server, calculate the tension force, compensate for the coefficient of elasticity of the tendon according to the ratio of the real-time elongation length data to the pressure data, and compensate for the tension force calculated.