The invention relates to an area-fixed edge computing system and a method for heterogeneous city internet of things, belonging to the technical field of the internet of things. The method comprises the following steps: S1, dividing the area into a plurality of virtual internet of things small grids according to the distribution density and position of GIS information and sensors in a specific areaof the city; S2, set at least one calculation point in each small mesh to be edge calculated, capture various sensor data in that small mesh, decoding the sensor data, calculating and screening out effective information, store, encrypting and uploading the information to a computing station; S3, combine a plurality of small grids into an enlarged grid, and arrange a computing station with multiple information sending and receiving and high computational power, picking up that uploading information of the computing points under the jurisdiction, classifying, analyzing and calculating, and deeply fusing heterogeneous information to generate imperceptible new information; S4: Upload the new information to the background server and download it to the application side. The invention converts the calculation of the edge into the calculation of the stationary type of the regional center, and improves the practicability and efficiency of the calculation of the edge of the urban internet of things.