In this paper, the rheology and printability of the PS@Ag/PDMS conductive paste were studied. The PS@Ag/PDMS conductive paste was fabricated by mixing the shell-core structured PS@Ag (silver nanoparticles coated on the polystyrene microspheres surfaces) hybrid conductive fillers with liquid polydimethylsiloxane (PDMS) prepolymer and its curing agent. The sandwiched flexible strain sensors of PDMS-PS@Ag/PDMSPDMS were fabricated by embedding the PS@Ag/PDMS composites in two PDMS encapsulated layers using printing technology and spinning coating process. The real-time monitoring results of the sandwiched flexible strain sensors in human body motions show that the relative changes of resistance of the flexible strain sensor in elbow joint and knee joint flexion-extension cycles can reach 0.75 and 0.50 respectively. The sensors show high stretchability, sensitivity and signal uniformity, which have great potentials in the application of human body motion monitoring.