A smart cushion based on single-mode-fiber-multimode-fiber-single-mode-fiber (SMS) with core-offset splicing, which can simultaneously realize human vital signs monitoring and activity monitoring, is proposed and experimentally demonstrated. The SMS structure is sandwiched between a piece of fiberglass mesh and a polyvinyl chloride (PVC) layer and then embedded in a common home or office cushion, which is the component of the proposed cushion. When people sit on the cushion placed on a chair, micro-strain induced by human activity including respiration, heartbeat and body movement will change the output light intensity of the fiber structure. By signal processing algorithms including filtering, fast Fourier transform (FFT) and feature extraction, the respiration rate (RR) and heartbeat rate (HR) can be obtained and human activity state on the cushion including nobody state, movement state and normal state can be judged. Furthermore, the performances of two memory foam cushions with different thicknesses are compared and proven to be both available. Such a smart portable cushion can realize real-time, noninvasive and highly sensitive monitoring of vital signs and activities within the accuracy of one second, especially for the elderly in nursing homes and office workers.