The invention discloses a method for preparing (Z)-3'-hydroxy radical -3,4,4',5-tetra- methoxyl diphenyl ethylene by the material of renewable natural plant resource. Naturally sourced 3,4,5-tri-methoxybenzaldehyde (a derivative extracted from Chinese gall) is taken as the raw material; and 3,4,5-tri-methoyl mandelic acid is obtained through a dichlorocarbene insertion reaction and is reduced to obtain 3,4,5-tri-methoyl phenylacetic acid. The compound can have a Perkin reaction with naturally sourced isovanillin to construct a cis-form diphenyl ethylene backbone, and the (Z)-3'-hydroxy radical -3,4,4',5-tetra- methoxyl diphenyl ethylene is obtained after a decarboxylic reaction. The method adopts the renewable resource-isovanillin and the 3,4,5-tri-methoxybenzaldehyde rich in China to replace increasingly exhausted petrochemical materials, thereby having a good sustainable development capability and remarkable economic, environmental and ecological benefits.