The invention relates to a guiding structure of an idler-wheel type tappet. The guiding structure is mainly characterized in that a guiding pin is installed inside a guiding pin installation hole, a check ring is installed at the position of a hole opening of the guiding pin installation hole, and the tappet is installed inside a tappet installation hole. The tappet comprises a tappet body, an idler wheel pin and an idler wheel. The idler wheel pin is installed inside the tappet body. The idler wheel is installed on the idler wheel pin. The idler wheel is contacted with an oil pump cam. The tappet body comprises an upper tappet body section and a lower tappet body section. The lower end portion of the upper tappet body section and the upper end portion of the lower tappet body section are integrally connected. On the cross section of the upper tappet body section, the outer circle of the lower tappet body section is in an arch shape. The plane corresponding to the middle chord of the arch shape is a guiding plane. The central angle corresponding to the arch shape is larger than 180 degrees and smaller than 360 degrees. The guiding pin and the guiding plane are in clearance fit. The guiding structure of the idler-wheel type tappet reduces abrasions among parts, reduces the machining difficulty and improves the reliability and the production rate.