The invention provides methods for preparing active peptide powders and chitins from shrimp and crab by-products, and belongs to the technical field of high efficiency processing of biological resources. The method comprises the following steps: extruding and crushing fresh shrimp and crab shells; immersing the shrimp and crab shells in water; adding proteases to conduct enzymatic treatment for two times after the shrimp and crab shells are subjected to extraction by using ultrasonic waves; leaching the second enzymatic hydrolysate after the enzymolysis; washing to obtain the neutral shrimp and crab shells after the second enzymatic hydrolysate is leached; adding an acid for decalcification treatment; cleaning and drying to obtain the chitins; mixing pasty proteins extruded in extruding and crushing and adipose tissues with the first enzymatic hydrolysate; conducting vacuum concentration treatment on the solution after the enzymolysis; obtaining the active peptide powders after spray drying. The methods for preparing the active peptide powders and the chitins provided by the invention can improve the utilization efficiency of the proteases to a maximum degree, and improve the concentration of protein peptides in the enzymatic hydrolysate.