Orbital period and multi-color light curves ' investigation of OW Leo are presented for the first time. The orbital period of OW Leo is corrected from P = 0.325545 days to P = 0.32554052 days in our work, and the observational data from the All-Sky Automated Survey for SuperNovae (ASAS-SN) are used to test the newly determined orbital period. Then, the phased light curves are calculated with the new period and the Wilson-Devinney program is applied to model the light curves, which reveal that OW Leo is a W-subtype shallow contact binary system (q = 3.05, f = 12.8 %). The absolute physical parameters of the two component stars are estimated to be M-1 = 0.31(1)M-circle dot, M-2 = 0.95(3)M-circle dot, R-1 = 0.63(1)R-circle dot, R-2 = 1.04(1)R-circle dot, L-1 = 0.43(1)L-circle dot and L-2 = 1.01(2)L-circle dot. The evolutionary status shows that the more massive star is less evolved than the less massive star. OW Leo has very low metal abundance, which means its formation and evolution are hardly influenced by any additional component. It is formed from an initially detached binary system through nuclear evolution and angular momentum loss via magnetic braking, and has passed a very long time of main sequence evolution.