Abstract: In this work, a prototype of time-of-flight detectors consisting of fast plastic scintillators coupled with fast photomultiplier tubes. The time performance of the detectors was tested using a picosecond pulsed laser, aiming at providing preliminary research for developing the time-of-flight detectors deployed at the future HIAF-HFRS. For two plastic scintillator detectors with different sizes, a systematic test was conducted by changing the parameters such as spot size, frequency, light intensity and hitting position of the laser to simulate the real ion-beam conditions. The tests were performed using a CAEN-DT5742 digitizer and a Mesytec-MCFD16+MTDC32 electronics system. When a focused laser was directed at the center of the plastic scintillator, the best time-of-flight (ToF) resolution achieved by the two small-size (7 cm×7 cm) plastic scintillator detectors was 8 ps; for the detectors with one small size and one large size (26 cm×10 cm), the optimal ToF resolution was 12 ps. When changing the parameters of the laser, the corresponding ToF resolutions were 10~16 ps and 19~46 ps, respectively. Our test results indicate that the achieved ToF resolution meets the requirements of the time resolution performance for the HFRS beamline, establishing the foundation for the optimization of the time-of-flight detectors.