Substrate is the key material of soilless culture. The physical and chemical properties of the solidified cultivation medium are good and relatively stable, and there is no need to use plastic cultivation containers in the cultivation process, which has a broad application prospect in three-dimensional greening and fruit and vegetable planting. We have developed a novel substrate solidified process with high-frequency electromagnetic heating, which significantly reduces energy consumption compared to the traditional curing process with steam heating. In this study, the effects of three modification methods (alkali modification, APTES modification, and alkali + APTES combined modification) on the physicochemical properties of jute were studied, and the strengthening effects of different modified jute fibers on solidification substrate were investigated. The results showed that the addition of jute fiber could improve the mechanical properties of the solidification substrate. Compared with the control group, the modified jute fiber could increase the breaking tension by 13.1~24.2 N, the impact toughness by 0.85~2.09 KJ/m², and the hardness by 21.6~35.6 HA. Moreover, the addition of a small amount of jute fiber can effectively improve the mechanical properties and will not affect the growth of plant roots.