Aiming at the enlarging scale of quantum logic circuits and the degradation of reliability, a new online error detection method based on single quantum gate is proposed. A new signal generation gate and an error detection gate are designed by the method and the parity-preserving characteristics are used to detect the error of the circuits. In the meantime, the method can detect the signal generation gate, ensuring the correctness of the gate. In addition, a new self-repairing method for quantum logic circuits based on hardware redundancy is given. The results show that the new method can detect all the error with less quantum gates and garbage outputs, and the first-realized self repairing method increases the fault-tolerance capability and reliability of the quantum circuits.