A conjugated reflectometer was designed to measure both the total hemispherical reflectance and the specular reflectance of samples in real-time, and it could also be used for temperature-dependent reflectance measurement. The primary component of the conjugated reflectometer is a hemi-ellipsoidal shape shell (axis ratio 10∶9∶9) with relatively high specular reflectance (>70% in the spectral ranges from visible light to long-wave infrared) on its inner surface. The measuring principle and configuration of the reflectometer were introduced. The main influencing factors of collection efficiency including the position of incident port, incident direction, incident beam diameter, collecting aperture, and the reflection property of interior surface of the hemi-ellipsoidal shell were analyzed and simulated by the ray tracing method qualitatively. Obtained results indicate that a collection efficiency of 97.8% ratio to entire collection can be obtained by the detecting laser beam with a diameter of 10 mm and collecting aperture of 38.1 mm. Furthermore, the higher degree of fineness is required for a shorter wave measurement; and the collection efficiency for certain area is mainly decided by the specular reflectance of inner surface with a perfect shape. It is concluded that the key factor for the accuracy and reliability of measurement is the machining precision of interior surface of hemi-ellipsoidal shell, therefore,the shape accuracy, degree of fineness and the reflectivity of inner surface are all very important.