Abstract: The vacuum isothermal forming of TC4 alloy thin shell was simulated numerically,and the relevant experiment was conducted according to the simulation result. The mechanical property,the microstructure and the content of foreign substances of the shell formed under vacuum isothermal condition were analyzed by taking those of the shell formed by hot stamping and the original TC4 alloy plate as references. The results showed that compared with shell from hot stamping,the content of H has a reduction of 83%,the content of O has a reduction of 50% and the elongation has an increase of 50%; the microstructure is homogeneous equiaxed structure.