The invention relates to a separation system, which comprises a gravity separation device and a post-treatment device, wherein the gravity separation device is used for separating a gas-liquid mixture including a first gas, a second gas and at least a liquid into a first gas phase including the first gas and the second gas, and a first liquid phase at least including the liquid, the post-treatment device is used for separating the first gas phase to obtain a second gas phase with enriched first gas and depleted second gas, the gravity separation device comprises a first separation unit for separating the gas-liquid mixture into a first light stream and a first heavy stream, the first separation unit comprises a first material feeding channel, a first upper channel and a first lower channel, and the gravity separation device further comprises a terminal upper separation unit communicated to the first upper channel and a terminal lower separation unit communicated to the first lower channel. The embodiments of the present invention further relate to a separation method.