The circular electron-positron collider (CEPC) requires a 3% precision in the measurement of d E/d xto identify long-lived charged particles. However, the measurement of d E/d xhas a blind area for each of charged particles of $\pi / \rm{K}$ , $\pi / \rm{P}$ , and $\rm{K} / \rm{P}$ , having transverse momenta of 1 GeV/ c, 1.6 GeV/ c, and 2 GeV/ crespectively. One potential solution is to use a high-precision time-of-flight (TOF) detector with a time resolution of less than 50 ps to fill in the blind area. To address this, we propose a small particle TOF detector that uses small plastic scintillators ( $1 \;\; \mathrm{cm} \times 1 \;\; \mathrm{cm} \times 0.3 \;\; \mathrm{cm}$ ) silicon photomultipliers for readout. In this work, we introduce the construction of the detector and calibrate its performance by using ${ }^{90} \mathrm{Sr} $ electron collimators and high-speed waveform acquisition electronics. Using a constant fraction timing method, we find that the time resolution of the detector is about 48 ps, satisfying the CEPC’s requirements for TOF detection.