The invention discloses a muscle stretching detector during limb rehabilitation training. The muscle stretching detector comprises a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a first capacitor, a second capacitor, a third capacitor, a fourth capacitor, a fifth capacitor, a first potentiometer, a second potentiometer, an adjustable capacitor, a capacitive displacement pressure sensor, a triode, a power supply, a time-based chip and a phase-locked loop integrated circuit, wherein the capacitive displacement pressure sensor transmits the signal of muscle movement condition during the limb rehabilitation training to the time-based chip, the signal is modulated by the time-based chip and input the phase-locked loop integrated circuit, the phase-locked loop integrated circuit generates direct-current output voltage, the fifth pin of the phase-locked loop integrated circuit outputs a muscle movement signal, and the muscle movement signal is output through the transmitted of the triode. The muscle stretching detector has the advantages that the movement condition of muscles can be detected in real time, and the muscle stretching detector is quite helpful for patients during the limb rehabilitation training.