Limited by the differences between cementitious materials and basic magnesium sulfate cement (BMSC), the study of enhancing the toughness and mechanical properties of BMSC products by incorporating bio-based fillers with fibers is still very limited. Through different mix design, wood fiber and basalt fiber (BF) were used as lightweight fillers and reinforcements of BMSC materials. The fluidity, dispersity (fiber), density, compressive strength and flexural strength of modified BMSC were tested. The typical samples were characterized by SEM, EDS and XRD. The results showed that the addition of wood fiber significantly reduces the density of BMSC, and the combination of wood fiber and BF can significantly improve the mechanical strength, especially the flexural strength, with the maximum increase rate of more than 80%. By microscopic characterization, it was found that wood fiber has good mixed compatibility with plant materials in BMSC. The combination of wood fiber and BF forms a magnesium cement matrix-wood fiber-BF model, which significantly improves the strength of the composite reinforcement. A semi-quantitative method based on image recognition technology was attempted, and it was found that the development degree of hydration products crystals could be analyzed quantitatively. It provides the possibility to control the performance of BMSC products during material preparation.