The invention discloses a preparation method and application of Z-3,4,4',5-tetramethoxy-2',3'-dihydroxy diphenylethylene. The preparation method comprises the following steps of: taking 2,3,4-trihydroxy phenylfluorone as a raw material; carrying out single methylation on the 2,3,4-trihydroxy phenylfluorone; carrying out substitution reaction on the methylated 2,3,4-trihydroxy phenylfluorone with bromopropane so as to obtain 2,3-diisopropoxy-4-methoxybenzaldehyde; carrying out Perkin reaction on 2,3-diisopropoxy-4-methoxybenzaldehyde with 3,4,5-trimethoxyphenylacetic acid so as to obtain E-2-(3,4,5-trimethoxyphenyl)-3-(2',3'-diisopropoxy-4'-methoxyphenyl)acrylic acid; carrying out decarboxylation to obtain Z-3,4,4',5-tetramethoxy-2',3'-diisopropoxy diphenylethylene; and finally obtaining Z-3,4,4',5-tetramethoxy-2',3'-dihydroxy diphenylethylene after carrying out deprotection. The synthetic route provided by the invention is simple and direct, cis-selectivity is higher, and the yield of the Perkin reaction as well as the total yield of Z-3,4,4',5-tetramethoxy-2',3'-dihydroxy diphenylethylene are both higher. The preparation method disclosed by the invention has the characteristics of simpleness and feasibility for operation, low price and easy obtainment of used raw materials and reagents, small pollution on environment, good atom economy, low cost and capability of being applied to industrialized production.