The invention relates to a preparation method of VI-type slowly-digestible starch. The preparation method comprises the following steps of: adding 0.3-0.8 percent by mass of monoglyceryl laurate ester into high-amylose corns serving as raw materials; dispersing a mixture obtained from the former step into 40 percent of ethanol solutions (w/v) of which the volume is seven times that of the mixture; dropwise adding 1.5mol/L of KOH solution (w/v) of which the volume is five times that of the mixture; at the end of reaction, performing heat non-crystallizing for 24 hours by using alkali in 1.5mol/L of citric acid neutralizing system after dehydration, desalination and impurity removal; and pulverizing and screening to obtain the VI-type slowly-digestible starch. An external digestion experiment result shows that the content of the VI-type slowly-digestible starch is about 78 percent; by using a differential scanning calorimeter and an X-ray diffraction technology, the analysis on heat stability and crystal forms of the VI-type slowly-digestible starch is carried out; and a result shows that the thermal decomposition temperature (Tp) of the VI-type slowly-digestible starch prepared by using the technology is up to 100 DEG C, and enthalpy change (delta H) is 20-23J.g-1; and moreover, the VI-type slowly-digestible starch belongs to a VI-type starch complex.