The invention relates to a truth-preserving sampling system and sampling method for a hydrate experiment loop. The system comprises two circuits, namely, a main experiment circuit and a sampling loop respectively, wherein the main experiment circuit is sequentially connected with a pump, a pressure transformer P-001 and an adjusting valve CV-001; the sampling loop is sequentially connected with an adjusting valve CV-002, a stop valve V-001, a stop valve V-002, a truth-preserving sampler, a stop valve V-003 and a stop valve V-004; the adjusting valve CV-002 is connected in the downstream position of the adjusting valve CV-001 on the main experiment circuit, and the stop valve V-004 is connected in the upstream position of the main experiment circuit; the main experiment circuit and the sampling loop are connected end to end to form a circulation loop. During sampling, valves on the sampling loop are opened, media are pumped to circulate in the circulation loop, after a period of time in the sampling loop, the media in the truth-preserving sampler have the same temperature pressure and composition as experiment media, and the purpose of truth-preserving sampling is achieved. The system realizes truth-preserving sampling of a natural gas experiment loop, and provides experiment samples for research of phase ingredients of natural gas hydrate in an experiment pipeline.