This paper describes analysis of the S parameter of an X-band (8-12GHz) Wilkinson power divider by using odd-even mode, as well as full circuit analysis technique. The closed-form model of the S parameters versus normalized frequency response of the power divider is proposed for the first time according to our acknowledgement. The expressions are compared with the results obtained from a full-wave electromagnetic simulator (ADS) and found to yield acceptable agreement: the insertion loss is -3dB, the maximum difference of return loss of port 1 and isolation is about 0.17dB, the return loss of port 2 is less than -38dB.