Several sets of blast model tests were conducted on dry sandy foundation with both normal gravity and supergravity, in order to investigate the effects of initial stress of sandy soil on the propagation characteristics of blast waves, such as peak pressure, rise time, propagation velocity, and dynamic unloading of initial stress. Experimental results showed that the initial self-weight stress inhibited the growth of the peak pressure of the blast wave in the near zone and had little effect on the far zone. The increase of initial stress made the rise time of the blast wave longer and more susceptible to attenuation from the shock wave into the elastic-plastic wave, and the propagation velocity of the blast wave was increased. The supergravity test could simulate the process of dynamic unloading caused by the blast load by restoring the original self-weight stress of the sandy soil, forming coupling wave of explosion pressure and soil initial stress dynamic unloading tensile stress. The dynamic unloading tensile stress lasted longer. The dynamic unloading tensile stress specific impulse magnitude gradually became the main part of the explosion energy with the increase of propagation distance, as compared to the specific impulse magnitude of the blast pressure. The damage effect caused by the dynamic unloading tensile stress specific impulse magnitude cannot be ignored.