Streak tube imaging lidar (STIL) is a new type of flash laser radar. The characteristic of STIL is wide field of view and high resolution. The exact streak data extraction is crucial in the three-dimensional reconstruction of the target. The deviation caused by the noise and CCD sampling has been ignored by the existing peak detection method. It causes deviation when the data of the streak image is extracted. Based on the analysis of the returned waveform and the theory waveform, a method of streak data extraction algorithm is presented and it not only eliminates the deviation but also filters the system noise effectively. A ladder imaging experiment is designed to verify the accuracy of the algorithm. It shows that this algorithm can improve the accuracy of streak data extraction obviously.