The invention provides a measurement device and method of injected gas-liquid phase diffusion coefficient for fracture-vug type oil reservoir. The measurement device comprises a constant-speed and constant-pressure pump, a piston intermediate container, a gas buffer tank, a reaction kettle, a thermostat and a pressure data processing unit; the constant-speed and constant-pressure pump, the pistonintermediate container, the gas buffer tank and the reaction kettle are orderly communicated; the piston intermediate container, the gas buffer tank and the reaction kettle are arranged in the thermostat; the pressure data processing unit is used for collecting and monitoring outlet pressure of the piston intermediate container, the outlet pressure of the gas buffer tank, and inlet pressure of thereaction kettle. Through the device provided by the invention, the measurement precision can be guaranteed when the injected gas is in diffusion by adding the gas buffer tank; an initial pressure value of the contact of the injected gas and liquid phase is obtained by adopting a gas state equation computation method, the measurement error is reduced, the nonlinear regression fitting is performedby cooperatively utilizing the Fick diffusion second law and a pressure failure curve so as to acquire the precise diffusion coefficient through computation, and the result has practical significance.