The invention relates to a vapor-liquid separation method of an evaporator and the evaporator, which comprises the following details: (1) both ends of at least a group of heat exchange tubes are respectively provided with a header; the two headers are provided with a plurality of leakage vapor resistance devices in an alternation way which can be embedded in the headers; the two headers are divided into a plurality of liquid separation spaces which are sequentially communicated; the leakage vapor resistance devices are provided with at least one valent weight main hole and a plurality of valent weight pilot holes; (2) when dropsy in the liquid separation spaces has few, a liquid membrane formed by the main hole and the pilot holes can prevent gas from entering into the liquid separation space of the next level header; (3) when dropsy in the liquid separation spaces has more, the dropsy firstly perforates the main hole and outflows; while the pilot holes is continously sealed by the liquid membrane formed by the top; (4) when the thickness of the dropsy layer in the liquid separation spaces enlarges, the dropsy gradually perforates the pilot holes and simultaneously outflows from the main hole and the pilot holes. The evaporator is the evaporator adopting the vapor-liquid separation method and the leakage vapor resistance devices and effectively solves the problem that the drainage amount in the evaporator of the prior art is limited.