Construction of mutant strain is an essential method in pathogenesis researches. The conventional method for Brucella unmarked deletion mutant construction is based on suicide plasmid, but the efficiency is very low. In the present study, we first optimized the electroporation parameters, and then, the cloning plasmid pEX18Gm containing sacB was successfully used to construct unmarked deletion mutant of the type IV secretion system. This indicated that by using conventional cloning plasmid as suicide plasmid in Brucella, unmarked deletion mutants can be constructed with high efficiency.