The invention belongs to the field of medicinal chemistry, and discloses a barbiturate compound, a preparing method and application thereof. Specifically, the invention relates to the compound as shown in formula I, and a medicinal usage thereof as a selective LSD1 reversible inhibitor, particular to the application in preparing of antitumor medicine. A test shows that the compound in formula I can efficiently reversibly inhibit LSD1 activity, and has a weak inhibition action for homologous proteins MAO-A and MAO-B, can intensively induce differentiation of leukemia cell NB4 and obviously enhance the methylation level of primers H3K4me1 and H3K4me2 of the LSD1.