Capturing the stimuli from ambient environment and having response are critical to exploring the world. This not only requires a complex integration of heterogeneous components but also lacks a direct interface between the (opto)electronics and the working environment. Moreover, all existing technologies require a power source, which complicates the system design and limits operation schemes. Stretchable electronic devices are particularly desirable for practical applications because of the high mechanical deformability and adaptability enabling their integration with three-dimensional biological systems. In this work, we built up a monolithic piezoelectric nanogenerator system as self-powered wearable devices for use in physiological detecting on human body. The stretchable electrodes were directly printed on soft substrates with designed patterns. Subsequently, two-dimensional ZnO nanosheets were selectively grown on electrodes without any decrease of electrode conductivity. ZnO nanosheets with thin thickness which is more flexible compared with common ZnO nanowires, can generated charges under tiny mechanically deformation and sustainably perform non-invasive physiological functions, e.g. detection of pulses, by harvesting power from human body. This research is expected to have a positive impact and immediate relevance to many societally pervasive areas, e.g. biomedical monitoring, consumer electronics, and human-machine interface.