Abstract: In order to give consideration to both of the precision and speed to improve the comprehensive properties of the detecting system, a new high-speed algorithm is proposed based on computation structure of correlation in digital lock-in detection and it is optimized by oversampling. The algorithm based on oversampling reduces the sampling frequency to four times of the frequency of an input signal. Thus, the digital lock-in algorithm can be implemented by the addition and subtraction operations of 4q points in q periods. This process eliminates almost all the multiplication operations compared with the traditional method. And the speed of the digital lock-in algorithm is greatly enhanced. Moreover, a correction factor is introduced to improve the error caused by down-sampling. The results of the experiments show that the new algorithm not only has high precision of oversampling and digital lock-in detection for signal with low signal-to-noise ratio, but also has high speed, which makes it possible for a general microprocessor to implement weak signal detection by the new algorithm in real time.