By setting up a fiber Bragg grating (FBG) displacement and strain sensing system, this paper experimentally investigates dynamic behaviors of a cantilever beam under impact or moving mass loadings. Dynamic sensing ability of the FBG displacement sensor is demonstrated by simultaneously measuring with a noncontact Fotonic sensor. Responses obtained from the FBG strain sensor are compared with those obtained from polyvinylidene fluoride film sensors and a strain gauge. First, an impact loading is generated by an impact hammer, and transient out-of-plane displacement responses obtained from the proposed FBG displacement sensor are compared with finite element simulations. Then, vibrations of the cantilever beam subjected to impact loadings by a steel ball are investigated. Finally, with a high-speed camera to detect the moving speed, experimental study of the cantilever beam under a moving mass is performed. By using the FBG displacement and strain sensing system, three kinds of modes of the cantilever beam (i.e., bending modes, lateral bending modes, and torsional modes) are detected under impact or moving mass loadings. With the high sensitivity of the proposed FBG sensing system, relationships between the transient responses induced by impact or moving mass loading and the vibration modes are discussed.