The traditional magnetic flux leakage(MFL) detection technology is difficult to meet the requirements of steel oil and gas pipeline crack detection, a new residual magnetic flux leakage(RMFL) detection technology was proposed, which directly used the residual magnetic state of the pipe wall after MFL detection to realize the effective detection of small opening cracks. Compared with magnetic leakage signal, remanent signal had lower signal-to-noise ratio and higher requirement on sampling frequency of sensor. Therefore, a spatial resolution method was proposed to optimize sampling frequency of remanent signal. Firstly, the dynamic magnetization model of pipeline was established by finite element simulation, the crack characteristic data was extracted, and the distribution law was analyzed. Secondly, the frequency domain analysis method was used to optimize the sampling frequency of residual magnetic signal. Finally, the effectiveness of the crack remanence detection method based on spatial resolution was verified by experiments. The results show that the remanent signal based on spatial resolution is highly consistent with the original signal, and there are undistorted sampling points at the poles of the signal waveform, which preserves the key features of the original signal and provides an important data basis for quantifying the crack size. This technology can realize the effective detection of cracks in small openings of pipelines, and has strong engineering practicality and operability, which is conducive to the further development of crack detection technology in oil and gas pipelines.