This invention relates to a method of in-situ remediation of arsenic-contaminated soil, comprising the following steps: inoculating a bacterial strain, Pseudomonas putida MnB1 in a culture medium where an addition amount of the bacterial strain accounts for 2-10% (v/v) of the culture medium; shaking the culture medium with the bacterial strain at a rotation speed of 100-180 rpm at 15-35° C. for 1-5 days under an aerobic condition, thereby yielding an enriched bacterial strain; and adding manganese carbonate, ammonium ferrous sulfate, sodium citrate, a yeast extract and the enriched bacterial strain to arsenic contaminated soil; adding water to the soil until the soil has a moisture content of 50-70%, stirring the soil for 5-30 minutes, and culturing the bacterial strain in the soil under an aerobic/microaerobic condition at 10-40° C. for 2-6 weeks.