With the construction of a number of massive projects, the structure failure becomes more common and will probably lead to huge economic losses and casualties. It has important and practical significance to establish a complete set of structural health monitoring system for these massive projects. Damage detection is one of the core technologies for structural health identification. Although a variety of damage identification methods have been developed, accurately measuring the response of the structural information is still the premise of the effectiveness of damage identification. Damage in the massive structures cannot be predicted, so it is not advisable to perform health monitoring by means of strain gauges. We use quasi-distributed long-gage optical fiber Bragg grating (FBG), combined with the damage detection application in simply supported steel-concrete composite beam, to verify the performance of such a sensor. The test results show that damage identification efficiency is reduced with the increase in length of the quasi-distributed long-gage FBG strain sensor gage.