There is a ubiquitous boundary reflection effect of stress wave propagation in the indoor experimental studies. It is critical to improve the validity of waveform data by optimizing boundary materials to absorb reflection waves. In the present study, a calculation method for the optimal wave impedance of boundary materials was proposed based on the transmission and reflection principle of one‐dimensional stress waves at the interface of different media. By using the calculation method, the optimal wave impedance value of the boundary material was obtained. A one‐dimensional stress wave propagation test apparatus was developed for exploring the improvement effect of absorbing materials on the boundary reflection effect. One‐dimensional stress wave propagation experimental studies in the complete red sandstone samples were carried out by setting various boundary absorbing materials such as pine pad, rubber pad, and steel pad. The results indicated that the experimental test results were consistent with the theoretical calculation results. In the stress wave propagation tests, the optimal wave impedance value of the boundary material was 1.12 × 10⁶ kg/m²·s. When the pine pads were used as boundary absorbing materials, the suppression effect of boundary reflection effects is relatively the best. The present study provides references for analyzing the characteristics and mechanism of stress wave propagation and attenuation.