The invention provides a low-temperature deep frying device and a method for deep frying food to be deep fried. The low-temperature deep frying device comprises a deep frying groove, a material inlet / outlet door, an oil inlet / outlet, a heating tube arranged in the deep drying groove, a vacuum device for making the interior of the deep frying groove reach a vacuum state, a deep frying main air cylinder for adjusting the deep frying position, a material inlet / outlet door air cylinder a for driving the material inlet / outlet door to descend or ascend, a material inlet / outlet door air cylinder b for driving the material inlet / outlet door to be opened or closed, an oil level meter for detecting the height of the oil level, a temperature gauge for detecting the oil temperature, and an electromagnetic valve used for receiving an oil temperature signal and controlling the deep frying main air cylinder, the material inlet / outlet door air cylinder a and the material inlet / outlet door air cylinder b, wherein the material inlet / outlet door and the oil inlet / outlet are communicated with the deep frying groove. According to the low-temperature deep frying device, the amount of oil injected into the deep frying groove and the temperature of the oil in the deep frying groove can be known through the oil level meter and the temperature gauge; through the deep frying main air cylinder, the position of a material inlet basket can be adjusted so that articles, to be deep fried, in the material inlet basket can make full contact with the oil.