The accurate and rapid detection of voltage and current in non-sinusoidal and unbalanced voltage condition is the prerequisite for grid power quality management and stable operation. Based on analyzing the vectors of the grid voltage and current, the rotating vector detection is carried out which can detect the voltage and current specified harmonic component and reactive and active current in non-sinusoidal and unbalanced voltage condition. The detection algorithm needs only the instantaneous value of voltage and current and no need the phase locking loop (PLL) to detect the voltage phase angle. The detection accuracy is not affected by the voltage frequency offset. The simulation results illustrate the accuracy of the rotating vector detection.