The original tube-in-tube microreactor allows the gas-liquid balance achieved in seconds, and the gas-liquid properties can be quickly measured through the online flow method. The software control function in the system can automatically record and save the temperature, pressure, liquid flow rate and gas flow rate of the measurement process. The working mode can be subgrouped to quasi-steady and unsteady mode with the relevant flow computation model which has been integrated into the software. The quasisteady mode can measure the solubility and diffusion coefficient of conventional gases in liquids; Non-steady mode can quickly determine the diffusion coefficient of gas in liquid, especially suitable for high viscosity systems such as ionic liquids.