The invention belongs to the field of medicinal chemistry, and discloses a 3, 6 modified-[1, 2, 4] triazole [3, 4-alpha] phthalazine compound having antitumor activity as well as a synthesizing method and application of the 3, 6 modified-[1, 2, 4] triazole [3, 4-alpha] phthalazine compound. The 3, 6 modified-[1, 2, 4] triazole [3, 4-alpha] phthalazine compound has a structure as shown in a general formula I, wherein R1 refers to H, methyl or phenyl; R2 refers to 4-fluorophenyl, 4-chloroanilino, 4-bromophenyl, 4-methoxyphenyl, 4-hydroxydiphenyl, 2-fluorophenyl, 3-trifluoromethyl)phenyl]amino, naphthylamine-1-yl, pyrrolidone-1-yl, piperidine-1-yl, 3,5-dimethyl piperidine-1-yl, morpholine-4-yl, or piperazidine-1-yl. The preliminary in-vitro antitumor activity finds that the serial compounds have obvious inhibit and killing effects on multiple tumor cells, and the 3, 6 modified-[1, 2, 4] triazole [3, 4-alpha] phthalazine compound can act as an active ingredient to be applied to clinical prevention and cancer treatment after being developed into a novel medicament.