The invention provides a detection method for a cooling slot gap of a flame tube of an engine. A detection tool kit adopted in the detection method comprises at least two detection tools, each of at least two detection tools comprises a flexible wire rod and a spherical structure which is attached to the flexible wire rod, and the spherical structures of different detection tools have different size specifications. The detection method comprises the following steps that two detection tools are selected from the detection tool kit, the diameter difference of the spherical structures of the twodetection tools is equal to a tolerance zone of an allowable value of the slot gap to be detected; and by dragging the flexible wire rods, the spherical structures of the two detection tools are madeto try passing through the slot gap to be detected.