Abstract: The degree of crushing blocks during open-air blasting is the primary measurement standard for comprehensive costs such as drilling, shoveling, transportation, and follow-up processes. Powder factor is the primary influencing factor and is typically used in blasting model tests to perform related research. However, high costs, test results for errors, and other shortcomings exist. Uniaxial compression, modulus of elasticity, fracture toughness, and other tests were conducted on the model materials based on the basic theory of explosive rock-breaking using basic mechanical testing equipment to calibrate the parameters of the riedel hiermaiver thoma (RHT) intrinsic model to optimize the powder factor of explosives to reduce the percentage of large blocks, reduce the average block size, and predict the block size of blasts in actual projects. Using the numerical simulation software LS-DYNA and the SPH particle flow algorithm to construct a three-dimensional open-air step blasting numerical simulation model, the numerical simulation results of blasting rock breakage to realize the block degree of accurate statistics and blasting rock breakage block degree with the powder factor rule of change were systematically performed. The results of this study show that when increasing the powder factor from 0.23 to 0.79 kg·m⁻³, the maximum block size is less than 240 mm and shows a different declining trend, which is divided into three zones of a similar decline in block size corresponding to the maximum block size gradient of 240, 220, and 140 mm, and two zones of a significant decline in the maximum block size with corresponding powder factors of 0.31–0.39 and 0.55–0.71 kg·m⁻³, respectively. The average block size shows an overall decreasing trend with an increasing powder factor of 0.23–0.55 kg·m⁻³, the average block size decreases from 120 mm to 67.7 mm, and the homogeneity index n decreases from 0.85 to 0.60. The fractal dimension D increases from 2.15 to 2.40. The powder factor is 0.55–0.79 kg·m⁻³, and the average block size fluctuates up and down, with maximum and minimum values of 76.83 and 65.65 mm, respectively. The homogeneity index n increases and then decreases, and the fractal dimension D decreases and then increases. The block size distribution pattern after blasting is consistent with the feedback from an actual engineering site, and the block size distribution curve of the powder factor is fitted using the G–G–S function. The correlation coefficients are between 0.91 and 0.97, verifying the feasibility and accuracy of the statistics of rock fragmentation block size in the blasting simulation results of the SPH method. This result overcomes the problems of high costs and large experimental errors in the traditional model test. The results of this study have specific significance for improving the distribution law of blast crushing bulkiness and bulkiness control engineering.