The microstructure of W and Ti alloy prepared by sintering and infiltration has been studied. The formation mechanism of W-Ti solid solution is discussed and the electron density of W-Ti solid solution is calculated by means of the Thomas-Fermi-Dirac-Cheng phase diagram (TFDC). The results show that the substitutional solid solution of TixW1-x results from the W and Ti atoms diffusing into each other during sintering and infiltration at 1750 ℃. The hardness value range of this solid solution is 3350～5280 MPa (HV0.1). The electron density of W-Ti solid solution is 2.4851×1029 /m3 and the calculated lattice parameter is 0.3140 nm