Wearable devices have a broad range of applications in health monitoring and human-machine interfaces. Flexible musical instruments are a promising entertainment device for relaxing the body and mind in current high-pressure environments. Here, a silicone-based triboelectric pressure sensor is developed to achieve a flexible keyboard for playing music. It has a gradient layered structure that progressively modulates the contact area to delay strain saturation, achieving a remarkable 40-fold enhancement in sensitivity over traditional planar structures, expanding the response range, and enabling the capture of the four basic elements of musical sound, namely pitch, intensity, duration, and timbre. To avoid interference from the body and environment, two shielding layers are also attached to the upper and lower parts of the main structure. Compared to common contact-separation structure without the gradient structure, the designed device exhibits clear and more detailed output signals, which are related to the pressing process and can express musical characteristics. Through quantitative testing, the device has demonstrated good linear range, flexibility, rapid response, and durability. Based on these features, a flexible keyboard for playing music is demonstrated. This work shows the potential of triboelectric sensors in wearable technology and human-machine interface fields.