The invention relates to a gas separating recycling system and a gas circuit for a mixed gas experiment. The gas separating recycling system comprises a gas separating pipeline, a gas separating device and separating gas storage tanks, wherein the gas separating device is arranged on the gas separating pipeline; the separating gas storage tanks are used for storing the separated gases; a gas tank gas-feeding pipeline which is communicated with each gas storage tank of a gas supply system is arranged on each separating gas storage tank or all the separating gas storage tanks are jointly communicated with a gas mixing tank; a communicating pipeline of a mixed gas experiment device which is communicated with the mixed gas experiment device is arranged on the gas mixing tank. When the mixed gas at different ratios is required by the experiment, the mixed gas is separated and purified through the gas separating recycling system and the separated gases are respectively stored in the corresponding separating gas storage tanks; the separated gases can be used as respective pure gas sources for the next experiment of the mixed gas; the experimental cost is greatly lowered and the environment is not polluted.