Abstract: Urban sensing, as the first layer of urban computing, is the foundation of intelligent cities, generating crucial data representing city dynamics for digital applications. Aiming to solve the challenges that urban sensing is facing, this paper proposes an urban sensing system that is comprised of a theoretical framework, a technical platform and an operational model. The theoretical framework consists of six categories of content to be sensed, four sensing paradigms, and four technical challenges. The technical platform provides digital tools for managing sensors and collecting data, and supplies upper-layer applications with interfaces for using urban sensing services. Urban sensing systems can reduce redundant sensor deployment and further operational workloads. It improves the capability of urban sensing service providers in solving problems and the synergy among each other. It also generates continuous economic benefits, such as income and employment, ensuring urban sensing functions stable and sustainable.