A photonic bandgap fiber collimator was proposed. To reduce the interference of light power from the echo, the return loss of fiber collimator should exceed 60 dB. There was no reflection in photonic bandgap fiber end face, thus the beveled angle of GRIN lens of photonic bandgap fiber collimator and ordinary fiber collimator satisfied the criterion were different. Based on the theory of matrix optics and Gaussian-beam coupling, the transform matrix was deduced from the general model of Gaussian-beam through a complex optical system. With the practical parameters of photonic bandgap fiber and GRIN lens, the influence of the distance between fiber tail and GRIN lens and the influence of the parameter of the GRIN lens on return-loss were both stimulated and analyzed. The results show that the return loss exceed 60 dB when the beveled angle of GRIN lens was 3°. The results may direct the design of PBF collimator.