The invention belongs to the field of high polymer materials and in particular relates to a polyamino acid block copolymer as well as a preparation method and application thereof. The polyamino acid block copolymer provided by the invention has a structure of a formula (I) or a formula (II), and hydrogel prepared by mixing the copolymer and a solvent has temperature sensitivity and is an aqueous solution at a relatively low temperature. When the temperature rises to be close to a body temperature, the aqueous solution can be changed into gel. Moreover, the hydrogel prepared by mixing the copolymer and the solvent has excellent biodegradability, the degradation period is about 2-15 weeks, the degradation products are amino acids and polyethylene glycol and can be directly discharged out of the body through kidney, and any adverse effect to the human body is avoided. The structural formula is as shown in the specification.