Effects of laser pulse width, laser intensity and rotational temperature on molecule alignment of N2O in monochromatic femtosecond laser pulse field are investigated theoretically. Influences of free parameters in laser field on molecule alignment of N2O are investigated in the following three cases. When the rotation temperature and laser intensity keep constant, only the pulse width is changed. When the temperature is constant, only the light intensity is changed at the same pulse width. When the pulse width and laser intensity are unchanged, only the rotational temperature is changed. Results show that by precisely adjusting the pulse width, laser intensity and rotational temperature, the molecular alignment can be enhanced or weakened.