The invention relates to the technical field of biological materials, and particularly relates to thermo-sensitive chitosan derivative-hydroxypentyl chitosan and a preparation method of the hydroxypentyl chitosan. The invention provides the preparation method of the thermo-sensitive chitosan derivative-hydroxypentyl chitosan. The method comprises the steps of firstly carrying out alkali activation on purified chitosan, then taking 1,2-pentane oxide as an etherifying agent, taking isopropanol as a dispersed phase, carrying out mild reaction for 3-6 days at room temperature, participating with acetone and washing until a neutral state reaches after reaction, carriying out vacuum drying in at 50 DEG C to obtain the hydroxypentyl chitosan. The hydroxypentyl chitosan disclosed by the invention has water-solubility and thermosensitivity; the lowest critical solution temperature (LCST) is 17 DEG C (2%W / V), and the hydroxypentyl chitosan can be fast cured into a stable gel state from a liquid state at physiological temperature of 37 DEG C.