The invention discloses a shape memory alloy based extension wing unfolding device, and relates to the field of flight adaptability of an aircraft in the complex airflow environment. An inner wing root is arranged on the edge of a fixed inner wing, the fixed inner wing is fixedly installed on the outer surface of the outer aircraft through the inner wing root; an inner wing beam is fixedly installed on the inner side of the inner wing root; the inner wing beam is fixedly connected with an outer wing beam; the outer wing beam is sleeved on the outer wall of the inner wing beam; a pulley is fixedly installed at one end of the outer wing beam; an extension outer wing is fixedly connected with the pulley; the two ends of a shape memory alloy wire are respectively fixedly connected with the two ends of the inner wing root, and are sleeved on the edge of the pulley. The shape memory alloy is used as a drive source, the elongation of the shape memory alloy wire is adjusted by changing the supply current of the shape memory alloy, the extension movement of an extension wing is realized through the match of the common spring and the shape memory alloy wire, and the problems that the current extension wing drive mechanism is huge and cannot be unfolded and shrunk for a plurality of times are solved.