In smart city, technologies such as blockchain, Internet of Things (IoT) and edge computing tend to be integrated that promotes horizontal information exchange and multi-party cooperation. Large amounts of superior services can be provided by analyzing the information. However, lots of IoT devices generating the information do not have sufficient resources to resist malicious attacks so that the devices deliberately upload the tampered data, which reduces quality of service. To solve the problem, we propose a data source trusted proof mechanism based on the node security measurement and threshold ring signature method. The mechanism firstly judges whether a node is in a trusted domain based on the proposed Distributed Sub-domain Networking (DSN) method to reduce energy consumption and avoid single point failure. Then, it quantifies security value of the nodes in the trusted domain based on the proposed three-dimension security measurement method. Finally, it confirms authenticity of the nodes using the Chinese Remainder Theorem (CRT)-based threshold ring signature scheme.Simulation results show our proposed mechanism can distinguish all malicious nodes among trusted nodes, the loss rate of trusted nodes is reduced to less than 5% and the false report rate is reduced to less than 10%.