Rainbow refractometry is a non-intrusive technology for determining the refractive index and diameter of liquid column simultaneously. An objective function is designed to quantify the deviation between the low frequency component of the captured rainbow and the simulated rainbow with Debye theory (p=2). Further, a novel inversion algorithm for liquid column based on Debye theory (p=2) and the objective function is proposed. Experiments are carried out to evaluate the performance of the algorithm. Results show that the relative error of the radius is less than 8%, the absolute error of the refractive index is less than 5×10-4 and the detection limit of the radius is as low as 60 μm with in the radius range of 50~500 μm and the refractive index range of 1.32~1.56.