The invention relates to a soft material sample cutting performance testing device and a testing method. Two guide posts are arranged between an upper box and a pedestal, a cutter component and a crossbeam component are slidably disposed on the two guide posts, the crossbeam component is driven by a control mechanism arranged in the upper box to slide up and down along the guide posts through a stay cable, the crossbeam component is equipped with an electromagnet for adsorbing the cutter component, and the work of the electromagnet is controlled by a PLC, thus achieving connection and disconnection of the crossbeam component and the cutter component. The device and the method provided by the invention utilize the principle of free fall, a fixed initial energy is set for sample cutting, the rest energy after cutting is measured, and then the energy difference before and after cutting is acquired, thus obtaining the total energy needed by sample cutting. The device and the method provided by the invention can be used for testing the cutting performance of corn, sugar cane, sesame, cotton, bast fiber and other crops' stalks, nylon and other materials.