IO Cnc was classified to be a new G-type (G0) W UMa-type eclipsing binary system.Our first multicolor photometric solutions show that IO Cnc is a new W-subtype shallow contact binary with a fill-out factor off =16.1％ and a low mass ratio ofq =3.12 (or 1/q =0.32).During orbital period investigations,a cyclic variation and a downward parabolic variation with a rate of (-1.28 ±-0.43) × 10-7 dyr-1 was discovered in the observed-calculated (O-C) curve.The cyclic variation was analyzed by the light travel time effect (LTTE) via a potential red dwarf companion star,an orbital semi-major axis shorter than 4.88 ±0.82 AU was obtained.Finally,we collect physical parameters of a sample of 50 G-type shallow contact binaries (f ≤ 20％),it is suggested that most of the G-type shallow contact binaries are undergoing a long-term and periodic orbital period changes,especially more systems show long-term decreases.The long-term orbital period decrease indicates that IO Cnc is in a mass transferring from the more massive component to the less massive one.With the long-term decrease of the orbital period,this shallow contact binary will evolve into a deeper contact one.