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 of f = 16.1% and a low mass ratio of q = 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) x 10(-7) d yr(-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.