Abstract: Against the increasing requirement of large-scale conditions, there is more demand of the measurement instruments. As an efficient approach of measuring cloud droplets, the measurement distance of the rainbow refractometry is generally less than 50 cm owing to the limitation of the aperture of the imaging system. The synthetic aperture rainbow refractometry is proposed to achieve long distance droplet measurement. Laser beams of multiple wavelengths are used to irradiate droplets and multiple rainbow signals are generated. The multiple rainbow signals are collected and combined into one signal and then inversed to obtain the droplet parameters. In this way, the measurement distance of the rainbow refractometry is increased to around 1.5 m, which breaks the aperture limit of the rainbow refractometry and enlarges its applicability. Based on this technique, the multi-wavelength synthetic aperture rainbow refractometer is developed and suitable for parameter measurement of droplets in the central region of large-scale facilities with instruments located outside. The synthetic aperture rainbow refractometry is verified to achieve long distance droplet measurement. The feasibility and accuracy of the multi-wavelength synthetic aperture rainbow refractometer were proved through experimental tests of water and ethanol droplets with different sizes and refractive indices. The sizes of water and ethanol droplets were within the range from 100 to 200 μm. The droplet size and refractive index uncertainties were within 5 μm and 8 × 10⁻⁴, respectively. Therefore, the multi-wavelength synthetic aperture rainbow refractometer is no longer limited by the aperture size and can be applied to larger industrial scenarios, achieving the multi-parameters droplet measurement of size, refractive index, and so on.