The invention relates to a short tubular starch nanocrystal and its preparation method, belonging to the field of carbohydrate nano-materials. The short tubular starch nanocrystal has an external diameter of 20 to 60 nm, wall thickness of 2 to 5 nm and a length of 3 to 6 nm and has the advantages of existence of cavity channels, a large specific surface area a regular structure compared with conventional flaky starch nanocrystals and granular starch nanocrystals. The preparation method comprises the following steps: subjecting native core starch particles to catalysis by dilute acid so as to dissolve most starch molecular chains in amorphous zones and preparing primary starch nanocrystals which are connected via the amorphous zones and can be bent; then allowing the primary starch nanocrystals to undergo self-assembling with the amorphous zones as bending points so as to form tubular-structured primary tubular starch nanocrystals; and subjecting the primary tubular starch nanocrystals to latency treatment at a low temperature for several days so as to allow starch nanocrystal sheets to be bonded via hydrogen bonds, and eliminating folding traces of connection of the starch nanocrystal sheets so as to form the polygonal short tubular starch nanocrystal with smooth transition angles.