Based on the analysis on LS-DYNA dynamic finite element, rotating fitting expansion tubular model was established with the whole expansion process simulation. By the analysis on stimulation results of different constraint methods to the tubular, it was found that the swelling force required in rotating fitting expansion is 1/5 of that in reverse tensile of solid cone; and change rule of axial length of the expansion tubular was variable in deferent constraint methods: with upper constraint method, the tubular length was a little decreased at first, and then steadily increased; while with underneath constraint method, the tubular length decreased all the time. This rule was proved by the rotary expansion test on Φ95mm tubular, the simulation was credible.