The invention provides an extraction method for high-purity high molecular weight chitin. The method comprises the following steps: (1) crushing insect chitin, adding into dilute acid, digesting for 4-6 hours at 30-50 DEG C, filtering, taking filter cake, washing with water and drying, thereby obtaining a decalcifying product A; (2) putting the decalcifying product A, complex enzyme and water into a reaction vessel, controlling reaction liquid PH at 7.5-8.5, stirring at 40-55 DEG C, hydrolyzing for 2-3 hours, and then filtering, taking the filter cake, washing with water and drying, thereby obtaining a deproteinization product B; (3) putting the deproteinization product B into a mixed solvent, adding neutral salt, dissolving for 1-3 hours by stirring at 60-80 DEG C, filtering, reducing pressure and drying the filtrate, removing solvent, washing with water, removing the neutral salt and drying, thereby obtaining the required chitin. According to the invention, the chitin extraction technique is simple, the device is conventional, the acid-alkali wastewater yield is low, the requirement for green and environment-friendly production is met and the obtained chitin is high in purity, high in molecular weight and low in ash content.