The invention discloses a preparation method of a copper extracting agent LPB. The preparation method comprises the steps of mixing 1,3-diphenyl-1,3-propanedione, mesitylene, 2-hydroxy-5-nonylacetophenone oxime and 15-crown-5 in a mole ratio of 1:1:(0.5-1):0.2, thus obtaining a main material of the extracting agent; mixing the main material of the extracting agent with kerosene in a volume ratio of 1:(4-9), thus obtaining the copper extracting agent LPB. The copper extracting agent LPB has the characteristics of relatively strong oxidation resistance, relatively wide feed liquid pH value application range, high efficiency and the like.