Abstract: In the characterization of infrared absorption spectroscopy, the sample is usually dealt with the KBr pressed pellet method, film transmission method, et al. Different preparation methods of coumarin sample including the KBr pressed pellet method, film transmission method and paraffin oil paste method are compared in this study. Compared with the KBr press pellet method, the film transmission method is more convenient and less amount of sample is need. Moreover, the film transmission method is recyclable and it can also avoid the fragmentation and sliminess in the process of sample pressing. Therefore, the high quality infrared spectra is obtained with the film transmission method.