In the article, a new idea has been brought out to study a traditional optical question, that is, fiber sensor was taken accounted as an information system, which has been analyzed with the information theory. The author began the analyses with the structure of the fiber sensor's core, i.e. microbend modulator, and then evaluated its performance with the amount and strengthens of the impossible acquired information. The infection of the modulator's characteristics has been discussed from the view of information theory, which has been proven by theoretically deducing and experimental data. As the result, the author advanced the opinion that method based on optics information theory can guide the process of the performance optimizing and the parameters designing.