The invention relates to an RNAi (
RNA interference) vector construction method and an application thereof in watermelon genetic transformation, relates to the technical field of 
plant virus control and belongs to the application technology in biological and modern 
agriculture technique fields. The mediated 
virus infection function is destroyed by acting on 
host factors and thus watermelons obtain antiviral activity, which has not been reported yet at present. An RNAi vector is constructed and genetically transformed to watermelons, the constructionmethod is characterized in that watermelon eIF4E and a homological isomer eIF(iso)4E 
gene thereof are cloned and connected, 4E-iso sense and antisense fragments are obtained and connected to two sides of an 
intron sequence, and a 4E-iso hairpin structure fragment is obtained; the 4E-iso sense fragment, the 4E-iso antisense fragment and the hairpin structure fragment are inserted into a pCAMBIA1301 vector through T4 connection and 
homologous recombination, and the RNAi vector is obtained; 
target gene fragments are transformed into watermelon 
cotyledon explants through 
agrobacterium tumefaciens-medicated transformation, and transgenic watermelons with the 
target gene fragments are obtained through screening cultivation. The method is mainly used for providing a novel material and a novel technology for watermelon 
virus and 
disease control.