Abstract: Flexible materials are essential in bionic fields such as soft robots. However, the lack of stiffness limits the mechanical performance of soft robots and makes them difficult to develop in many extreme working conditions, such as lifting and excavation operations. To address this issue, we prepared a stiffness-tunable composite by dispersing low-melting-point alloy into thermosetting epoxy resin. A dramatic and rapid change in stiffness was achieved by changing the state of matter at lower temperatures, and accurate control of the composite modulus was achieved by controlling the temperature. When the alloy content is at 30vol%, the tensile modulus changes 41.6 times, while the compressive modulus changes 58.9 times. By applying the composite to a flexible actuator, the initial stiffness of the actuator was improved by 124 times, reaching 332 mN/mm. In addition, the use of stiffness-tunable materials in the wheel allowed for timely changes in the grounding area to improve friction. These flexible materials with manageable mechanical properties have wide applicability in fields including bionics, robotics, and sensing. Our findings provide a new approach to designing and developing flexible materials with improved stiffness and controllability