The invention relates to a prompting dynamic wheel load meter. A longitudinal motion device comprises: a lower frame, a notch-type pivoting section I, a notch-type pivoting section II, a piston, a connecting frame and a foot support; the lower frame is arranged on a weight sensor; the two ends of the notch-type pivoting section I and the notch-type pivoting section II are respectively pivoted on the lower frame and the connecting frame, the other two ends of the notch-type pivoting section I and the notch-type pivoting section II are respectively operatively connected with the lower frame andthe connecting frame, and the piston drives the notch-type pivoting section I and the notch-type pivoting section II to pull the connecting frame to operate longitudinally. Thereby, the defects that the working cycle is reduced under the condition of excessive weight and no prompting function is provided in the prior art can be effectively avoided.