In this study, the main factors inlfuencing the measurements by means of the off-line low-ifeld 1H NMR in the lab were discussed base on a robust calibration model established by the PLS algorithm using 255 crude oil samples. The preheat-ing temperature had a great inlfuence on the viscosity of oil samples and the resolution of spectral analysis. The repeatability of spectral measurements was impacted by the metal and wax content of the oil samples. For the case of high wax content oils, the wax species began to crystallize in the course of determination that could affect the repeatability of spectral measurements. These factors have evidenced why the preheating devices and iflter unit are necessary when low ifeld NMR system is used in the online analysis process. The investigation is very important for the on-line application of the low ifeld NMR.