The temporal variation and the spatial distribution of the urban heat island in Shenzhen metropolis are studied based on the air temperature data from 103 automatic weather stations. The analysis shows that: 1) The rapid urbanization process in Shenzhen had changed the land cover type around some weather stations, which had had obvious impact on the air temperature data colleted by these weather stations over recent 10 years. 2) Shenzhen locates in seashore area and the distribution of the air temperature in Shenzhen is a compositive phenomenon caused by the urban heat island effect and the landsea effect. A new urban heat island index, namely, population weighted urban heat island (PWUHI) is designed, which is more temporally stable than the traditional urban heat island index and can be used in the municipal management.