Unsteady simulation research on temperature characterization in the collection tank of pVTt gas flow calibration facility is carried out.Calibration principle of pVTt is introduced.3D model is built up in nature environment and water-bath condition respectively.The time-varying characteristic of temperature field is calculated by fluent-software

from intake process to homogeneity period orderly.The simulation data is analyzed and ideas is presented about how to lay the thermocouple point.The result shows that temperature stabilisation period shortened from 436s in nature environment to water-bath’s 201s

which indicates water-bath greatly speeds up the temperature field stable process.Steady temperature field in water-bath condition distributes symmetrically with the axis of the tank

where the maximum temperature difference is less than 0.01K

and the serious temperature gradient existed in nature environment disappeared.