In order to explore the oil reducing mechanism of sodium alginate (AG) and low methoxyl pectin (LMP) on the fried sweet potato starch, the oil content, distribution and thermal properties of fried sweet potato starch with 0.5% (W/W), 2% (W/W) AG or 2% (W/W) LMP were investigated by low field nuclear magnetic resonance, confocal laser scanning microscopy, X-ray diffractometer, Fourier transform infrared spectroscopic analysis and differential scanning calorimetric analysis, respectively. The results showed that the total oil content of fried sweet potato starch significantly decreased with adding AG or LMP, while most of the oil was distributed on the starch surface. The crystallization pattern of fried sweet potato starch with adding AG or LMP changed from A+V type to V type, as well as the gelatinization enthalpy and relative crystallinity significantly decreased. The fried sweet potato starch with AG showed an obviously lower total oil content, relative crystallinity and gelatinization enthalpy than that with LMP. The fried sweet potato starch with 2% AG exhibited the highest gelatinization degree to form a continuous and dense lamellar structure, while showed the lowest total oil content and surface oil content. The result of this study could provide a reference for processing the fried starchy foods with low oil content.