The invention discloses a variable-length connecting rod variable-compression-ratio mechanism with a feedback device. The mechanism comprises a connecting rod upper part, a miniature rebound type displacement sensor, a stepped sleeve, a limit screw, an H-shaped double-thread rotor, a connecting rod middle part, a T-shaped bolt, a motor, a Hall encoder, a connecting rod lower part and a connectingrod bolt. The mechanism is characterized in that a connecting rod is divided into three parts, the Hall encoder is installed on the connecting rod lower part, the motor is installed on the connectingrod middle part, a motor output shaft and the H-shaped double-thread rotor are connected, and the H-shaped double-thread rotor is connected to the T-shaped bolt and the connecting rod upper part through upper reverse threads and lower reverse threads. The miniature rebound type displacement sensor is installed in a blind hole in the connecting rod upper part, the lower end is in contact with the motor output shaft for positioning, the changed length of the connecting rod is measured in the up-and-down moving process of the connecting rod upper part, the length change amount is transmitted to amotor control unit through a tail end signal line, and the motor control unit controls the compression ratio change in real time through a feedback signal.