A novel method of bandwidth enhancement of a chaotic carrier from a semiconductor laser transmitter is studied by cross-phase modulation (XPM). And a physical model of laser dynamics is presented under the condition of XPM effect of optical fiber path. A frequency detuning formula with optical dual-feedback and XPM effect is deduced. The nonlinear phase shift arisen from XPM effect impacts on the gain and bandwidth enhancement factor of the laser. The second order nonlinear effect of the fiber enriches the varieties in the amplitude and the phase of the laser while the nonlinear phase shift produces a lot of new frequencies, which spread the bandwidth. Numerical results reveal that, with XPM effect, the new bandwidth is the quadruple of the bandwidth without XPM effect, and the relaxation oscillation frequency of the chaotic laser is increased to 285 times that of the laser without XPM effect. It is found that the enhancement of the chaotic bandwidth depends evidently on the optical fiber length, the power input into the optical fiber, the mirror reflectance and the second order nonlinear coefficient.