Abstract: Quinn algorithm is a low computational complexity and steady method which is widely used in frequency estimation of single real sinusoid in additive white Gaussian noise is given, But it has a problem of large variance of frequency estimation when the signal frequency is closed to the DFT (Discrete Fourier Transform) discrete frequency in low SNR (Signal Noise Ratio); However， compared to Quinn algorithm ,the window-length changing phase difference correction algorithm has good frequency estimation precision in this case. But it also has a problem of large variance when the signal frequency is closed to the midpoint areas of two neighboring DFT discrete frequencies; Aimed at the characteristic, this paper proposes a combined algorithm which is based on Quinn algorithm and a window-length changing phase difference correction algorithm. the theoretical calculation process and related error formula are given out. From the result of computer Monte-Carlo simulation experiment and performance analysis,We can see that the new algorithm has higher accuracy and stability in the frequency estimation as well as low SNR threshold in the setting frequency range without increasing the calculation amount obviously. Its RMSE (Root Mean Square Error) is close to CRLB(Cramer-Rao Lower Bound) in the whole frequency range. the performance of the new algorithm is better than Quinn algorithm and window-length changing phase difference correction algorithm, So it has some practical value for engineering.