Abstract: The variance-covariance matrices of station coordinates can be rigorously transformed between two reference frames at the same epoch,ignoring the influence of velocities and 7 transform parameters rates.By the method,local area data can be brought into ITRF and avoid data processing repeat simultaneity.Moreover it's convenient to use directly international data products existed in the Internet.Analyzing the results of the example,discover that the transformed coordinates deviation can excel 0.1 mm level,which can meet the transformation request between two reference frames.This paper can be used for reference to unite data in different reference frames.