In accordance with the relevant safety standard requirements for electrical equipment, this thesis proposes a residual voltage detection method with high accuracy and low power consumption . The power frequency synchronization signal is obtained by the measuring instrument with the zero-crossing detection circuit used. In the power frequency AC peak moment the measured instrument's power is cut off and the measured equipment's residual voltage is sampled by the input circuit with the high input impedance. Under the control of the NIOSII, the on-line detection of power-down residual voltage of equipment after the 1second and 10seconds is realized with the high speed sampling /hold-circuit and high precision ADC module used. The experimental result shows that the measuring instrument has good stability, with measurement accuracy up to 0.506%, meeting the measurement requirements.