A portable retroreflection coefficient detector was designed according to relevant national standards to measure the retroreflection coefficients of the traffic signs, vehicle body markings and high visibility warning clothes. The measuring principles of retroreflection coefficients were analyzed and compared, and the retroreflection coefficient detector was developed based on the relative measurement method. White reflecting light was used as the divergent light source of the retroreflection coefficient detector, and it could simulate the actual working condition of retroreflection objectives in a short distance and to complete the measurement of the retroreflection coefficients. The designs of optical system, photoelectric conversion circuit and STM32F103C8T6 single-chip control system in the detector were introduced. A selection model for the test angles of retroreflection coefficients was established based on minimum safety driving distance, and the uncertainty of the retroreflection coefficient detector was evaluated. Finally, a test experiment was performed by using the portable retroreflection coefficient detector. The experiment results show that the maximum value of the indication error is 4.40% in the test range of (0.1-199.9) cd·lx-1·m-2 , and that is 1.31% in the test range greater than 199.9 cd·lx-1·m-2,which meets the requirement of GB 26377-2010 for indication errors. The portable retroreflection coefficient detector has advantages of miniaturization and intellectualization and has practical significance to detect the traffic safety signs and vehicle body signs.