Abstract: Solutions of the sweet potato blast bacteria (pseudomonas sola-nacearvm Smith) were inoculated to leaf pulp tissues of tomato, an indicator plant of the bacterium, with injection-infiltration in different conditions. The results showed that the period of occura-nce, the amount of the oozes and necrotic spots were chiefly determined by the concentrations of inocula, affected by temperature when it rose above 30℃ or decreased below 30℃ and retarded by light. Tender leaves beneath the terminal bud were the most susceptible to the bacteria. The incubation period in the plants by strains with stronger pathogenicity was slightly shorter.Samples of sweet potato seedlings, soils, waters and animal manures were ollected from diseased areas for detection. The Results indicated that the rate of bacterium-bearing was high in both of the sweet potato fields with high disease rate and the fields of their after-reap fall-sown soybean, moderate in their after-reap sugarcane and rare in their after-reap rice. High rate of bacterium-bearing was found in the sweet potato plants with clear symptoms, but low in the plants with no evident symptoms. High rate of bacterium-bearing was also found in the pitch waters of diseased fields and the dung excreated by pigs that had Keen fed with diseased plants. The above method was therefore concluded to be a quick and effective way to detect the sweet potato blast bacteria from various infection sources.