The invention provides a peach bacterial canker diagnosis method, which is characterized in that the method comprises the following steps: (1), taking diseased branches with visible dense small black spots and cutting out 5-8cm; (2), cultivating the peach branches at the humidity larger than 75% and smaller than 10% and the temperature higher than 10 DEG C and lower than 40 DEG C for at least oneday; and (3), determining the peach bacterial canker if conidium liquid appears on the small black spots on the peach branches. Whether the peach branches are infected with the bacterial canker can be diagnosed easily and quickly by the method, and expensive laboratory equipment and professional technical backgrounds are not needed.