The present disclosure discloses a 690 MPa high-strength medium-manganese steel with low yield ratio and medium thickness and a manufacture method thereof, which relates to the technical field of steel smelting. The 690 MPa high-strength medium-manganese steel with low yield ratio and medium thickness is composed of the following chemical composition in mass percentage: C: 0.05%-0.10%, Mn: 4.1%-4.7%, Si: 0.15%-0.4%, P≤0.010%, S≤0.003%, Ti: 0.01%-0.05%, Ni+Cr+Mo≤0.6%, and the balance of Fe and unavoidable impurities. The steel plate manufactured meets the safety performance and construction cost requirements of the construction machinery on the ultra-high-strength steel in complex environments.