Accurate and fast estimation of frequency and amplitude is crucial for smart grid monitoring and operation, and the spectrum leakage will seriously affect the measurement accuracy of frequency and amplitude. For this reason, a real-time frequency and amplitude measurement algorithm based on improved discrete Fourier transform (discrete Fourier transformation, DFT) is proposed. Firstly, the DFT algorithm considering frequency offset is deduced theoretically. Then, in order to reduce the effect of spectrum leakage, the results of DFT transform are recalculated. The expressions of frequency and amplitude are given. In order to further improve the accuracy, the frequency value is estimated two times. Simulation results show that the proposed algorithm can effectively reduce the influence of spectrum leakage on frequency and amplitude measurements, and can calculate the required frequency and amplitude under different signal models.