A novel ultra-long-period fiber grating with periods up to several millimeters induced by using CO2 laser pulses is reported and discussed based on the mode coupling theory. The refractive index change occurs mainly within the cladding area of the fiber and has an unsymmetrical distribution on the cross-section of the ULPFG. The characteristics of temperature, strain, torsion and the effect of the refractive index of environment were investigated in theory and by experiment. The experimental results showed that different resonant peaks of the ULPFG have different sensitivities in the characteristics above mentioned, which offers possible applications in optical communications and sensing.