Characteristics of scattering intensity distributions of the first and second order rainbows of graded-index polymer optical fiber (GI-POF) are studied by Lorenz-Mie theory and Debye series.By using low pass filter,band filter and inverse fast Fourie transform to the interference intensity distributions of different order rainbows,the contributions of each order can to recogniyed.The result conforms to the simulations of Debye series well.Twin first order rainbows are discussed,and the corresponding scattering intensity distributions are simulated by Lorenz-Mie theory and Debye series.