A method of wastewater treatment using a membrane bioreactor, including: controlling aeration to enable a dissolved oxygen concentration to be 0 to 1.5 mg/L, and keeping the integrated reaction vessel under a facultative environment. A wastewater treatment system by the membrane bioreactor without physical area division includes a reaction vessel, a membrane separation system, a water production system, and an aeration system. The membrane separation system is disposed inside the reaction vessel. The water production system communicates with the membrane separation system to pump filtrate out of the membrane separation system. The aeration system is employed to aerate the reaction vessel and the membrane separation system.