Developing fluid velocity sensors with high accuracy, high stability and self-power has practical significance. Triboelectric sensors provide a strategy to realize high-performance self-powered active sensing. In this article, we present a fully enclosed self-powered active spherical triboelectric sensor (SASTS) to detect the fluid velocity. Based on the electrification at the contact interface, resulting in the electrostatic induced electrons transferring between two interdigitated electrodes, SASTS effectively harvests the fluid flow energy to electric signal. After Fourier transform processing of the output signal, the motion frequency of the SASTS can be distinguished and the fluid velocity can be further calculated. By optimizing the structure parameter, it features high precision with average standard deviation less than 4, wide range speed from 2 m/s to 18 m/s of fluid flow, and proved lifetime more than half a year. This technique can be applied to measurement of fluid flow speed, even potentially to other rotation movements, which could have wide applications, such as environment monitoring, transportation and so on.