The invention provides a supporting device of a tachometer wheel, which can solve the technical problem that a telescopic rod in the prior art is easy to buckle with a fixing sleeve, and the normal speed measurement is influenced. The supporting device comprises a vehicle connecting base, a tachometer wheel bracket and a spring; the supporting device is characterized in that the vehicle connecting base comprises a base body, a base body fixing plate and connecting plates; the guide block is fixed at the lower part of the base body, and downwards provided with a guide part in a convex form; the guide part has an arc inner concave guide face and an arc chute extended along with the guide face; the lower end opening of the chute is sealed, a pair of connecting plates are distributed at both sides of the chute on width direction, and fixedly connected with the guide block; the upper end of the tachometer wheel bracket is pivoted and connected with the connecting plates at both sides through a rotary shaft; the top part of the tachometer wheel bracket is provided with an arc outer convex guide face and a slide block arranged in the middle of the outer convex guide face; the outer convex guide face is matched with the inner concave guide face; the slide block is glidingly connected to the chute; the spring is placed in the chute, and both ends thereof are leaned against the sealing parts of the lower parts of the slide block and the chute.