The invention relates to a method for recycling hydroxyproline wastewater, in particular to a method for preparing L-alanine by taking hydroxyproline process wastewater as a raw material. L-alanine is prepared by taking the hydroxyproline wastewater as the raw material through a high-temperature oxidization method and then separated and purified through the coupling processes of activated carbon decoloration and concentration, alcohol solution separation and alcohol (ketone) solution recrystallization. It is determined that the obtained product is a pure L-alanine product through nuclear-magnetic analysis and specific rotation determination. According to the method, wastewater recycling is achieved, the wastewater treatment cost is reduced, and the sustainable development goal of resources and environment is achieved.