The effects of prestrain, strain rate, and temperature on the impact properties of 304L stainless steel are investigated using a compressive split-Hopkinson pressure bar. The impact tests are performed at strain rates ranging from 2000 to 6000 s−1 and temperatures of 300, 500, and 800 °C using 304L specimens with prestrains of 0.15 or 0.5. The results show that the flow stress, work-hardening rate, and strain rate sensitivity increase with increasing strain rate or decreasing temperature. As the prestrain increases, the flow stress and strain rate sensitivity increase, but the work-hardening rate decreases. The temperature sensitivity increases with an increasing strain rate, temperature, and prestrain. Overall, the effects of prestrain on the impact properties of the tested specimens dominate those of the strain rate or temperature, respectively. Finally, optical microscopy observations reveal that the specimens fracture primarily as the result of the formation of adiabatic shear bands.