Abstract: This paper lays emphasis upon reference datum of dynmic geodetic network.Included in this paper are the discussion of the relation between the adjustment of free network and reference datum,the derivation of a general estimation formula of the coordinate parameters of arbitrary reference datum of free network,and the derivation of the transformation formula of the coordinate parameters and its cofactor matrix from the theory of reference datum.In addition,a procedure for analysis of displacement has been proposed,a practical example has been illustrated and the influence of different reference datum to the solution of displacement has been explained.