The present disclosure relates to a quantum dot light-emitting layer, a quantum dot light-emitting device and preparing methods therefor and belongs to the field of liquid crystal display. The preparing method for a quantum dot light-emitting layer includes: placing a first halide AX and a second halide BX2 in a solvent; stirring and dispersing the reaction system formed by the first halide AX, the second halide BX2 and the solvent at a set temperature for a set time period; cooling the reaction system at a cooling rate of 0.1° C./24 h-1° C./24 h to generate an A4BX6 single crystal thin film containing ABX3 quantum dots, and using the A4BX6 single crystal thin film containing ABX3 quantum dots as the quantum dot light-emitting layer; wherein A includes one of Cs+, CH3NH3+ and HC(NH2)2+; B includes one of Pb2+ and Sn2+; and X includes one of Cl−, Br− and I−.