The invention discloses a detecting template for an outer circle diameter of a crankshaft shoulder and a using method thereof. The detecting template is an inverted T-shaped plate, the inverted T-shaped plate has a horizontal bottom plate and a vertical plate perpendicular to the bottom plate, and detecting grooves for determining the outer circle diameter of the crankshaft shoulder are symmetrically laterally formed on two sides of the bottom plate; the detecting groove comprises an upper detecting surface and a lower detecting surface, the upper detecting surface is a maximum limit size of the outer circle diameter of the detected crankshaft shoulder, and the lower detecting surface is a minimum limit size of the outer circle diameter of the detected crankshaft shoulder; the width of thedetecting groove is equal to the difference between the maximum limit size of the outer circle diameter of the detected crankshaft shoulder and the minimum limit size of the outer circle diameter ofthe detected crankshaft shoulder; and the depth of the detecting groove is 3-8 mm. The detecting template is simple in structure and convenient and quick in operation, and has low requirements for skills of detecting personnel. The detecting template can be used for quickly determining the diameter of any position of the whole outer circle of the shoulder with high identification correctness and efficiency, and is suitable for popularization in large-scale industrial production.