Power consumption is a crucial parameter for wearable sensors to approach practical applications. As an ideal candidate for low consumption device, a capacitive pressure sensor can make up for the defects of low capacitance and sensitivity by introducing the iontronic sensing mechanism and can further improve the sensing performance through the construction of micro–nano structures at electrode–electrolyte interface. To explore a facile-effective microstructure construction method for promoting the mass manufacturing and cost reduction, in this study, an easily prepared ionic cellulose nanopaper (CNP) is served as a dielectric layer and sandwiched between two graphite paper electrodes. The combination of the CNP and graphite paper provides a typical microstructure interface, and the device is endowed with the characteristics of ultralight and ultrathin. The iontronic paper-based pressure (IPBP) sensor exhibits a high sensitivity of 67.5 kPa −1 and an excellent linearity above 0.99 over a broad pressure range of 0–30 kPa, and a low detection limit of 0.5 Pa, together with good mechanical stability for over 3000 loading–unloading cycles. Finally, the applications of the IPBP sensor for monitoring of human motion and physiological signals, such as joint bending, walking state, radial artery, and breathing, are demonstrated, which proves the great potential in wearable electronics, human health monitoring, and human–computer interface.