The invention discloses a method for simultaneous measurement of sound velocity of a multi-step horizontal rock body. The method comprises the steps: taking explosion of an explosive at the bottom of a test blast hole as a vibration source, adopting vibration measurers arranged at the middle-lower parts of different horizontal stepped slopes, acquiring surrounding rock vibration signals of vibration measuring points corresponding to the vibration measurers, dividing the distance difference of two corresponding vibration measuring points from an initial vibration source position by the relative time difference of the vibration signals reaching the vibration measuring points, calculating to obtain the sound velocity of the corresponding region rock body, so as to realize simultaneous measurement of the sound velocity of the multi-step horizontal rock body. The method is applicable to on-site simultaneous measurement of the sound velocity of the multi-step horizontal rock body, calculates and detects the cracking degree of the rock body, provides a basis for side slope stability analysis, side slope reinforcement scheme design and side slope forming blasting design, can also be used in open-pit mine blasting engineering or trench excavation engineering, and obtains the wave impedance matching condition between the explosive and rock in the process of construction, so as to provide a basis for optimization of explosive types, design of explosive performance and adjustment of charging parameters.