The invention relates to a microorganism method for detecting metallic-arsenic-like in water, in particular to an escherichia coli report bacterial strain culturing method improved through genetic engineering, and an escherichia coli culturing method for detecting arsenic in water. The detection bacterial strain is obtained by adopting a Red recombination system to knockout arsenic resistant arsB genes of wild type escherichia coli MC4100, and then adopting the gene knockin technology to substitute pars-arsR-gfpmut2 report genes to the positions of araB coding genes. The biological detection bacterial strain is named as E.coli WMC-011p. The lowest arsenic detection range meets the Integrated Wastewater Discharge Standard of GB8978-1996. The bacterial strain overcomes the shortcomings of high fluorescence background value, unstable detection signals, inaccurate results and the like of a biological detection bacterial strain based on a plasmid vector, and has the advantages of high specificity, high sensitivity, low cost and the like.