The invention discloses a synthetic method of a 1,2-bis(3-methyllphenoxy)ethane thermosensitive sensitizer. The method employs meta-cresol and dichloroethane as raw materials for production, and realizes combination of the two through usage of a phase-transfer catalyst. The invention has advantages of mild reaction condition, a highest temperature controlled at 100 DEG C, easily reached conditions, a short reaction time of a dozen hours, and a high product purity reaching higher than 99%.