In order to measure the grating constants of the plain rainbow holographic materials quickly and conveniently, the spectrophotometers (loop light illumination) and scanning equipments commonly used in color measurement fields are used to collect the spectral energy and image information of different plain rainbow holographic materials by fixing the measuring point and rotating the plain rainbow holographic materials in the range of 0°-90°. It is found that with the change of rotation angle, the spectral energy and image color information of the plain rainbow holographic materials collected in the range of 0°-45° and 45°-90° show a periodic and symmetrical change. From the grating equation, it is found that there are two effective grating constants in the side length and diagonal directions of the holographic master materials. The experimental results are in good consistency with those obtained by high amplification ratio microscopes. The measured results can provide a theoretical basis for the examination of the microstructures of light pillar holographic materials and plain rainbow holographic materials.