Abstract: 【Objective】 Consecutive mono-culturing of tomato seriously affects its yield and quality in the protected tomato production in China. Tomato and onion intercropping is found effective in increasing tomato production, decreasing soil-borne disease and keeping healthy soil. Here the effect of theirintercropping on tomato(Lycopersicon esculentum Mill.) and tillered onion(Allium cepa var. agrogatum Don.)growth, mineral nutrient absorption and tomato gray mould disease incidence was studied. 【Methods】 A pot experiment was conducted in green house in 2012. Three culture modes were desinged: tomato and tillered onion intercropping, tomato monoculture and tillered onion monoculture. The growth indicators of tomato and tillered onion were investigated; the incidence and disease index of tomato gray mould disease were measured 30 days after the intercropping. The contents of total nitrogen, phosphorus, potassium and manganese were measured. The soil samples of rhizosphere of tomato and tillered onion were collected and the physical and chemical properties were measured. The activities of urease, acid phosphatase, dehydrogenase and polyphenol oxidase were measured using fresh soil samples which were stored in 4℃. 【Results】 1) Compared with the monocultures, the intercropping increases tomato plant height, shoot and root dry weights, and root activity significantly(P0.05), decreases those of tillered onion significantly(P0.05). The activities of soil dehydrogenase and polyphenol oxidase in the tomato rhizosphere are increased significantly(P0.05), while those in the tillered onion rhizosphere are decreased significantly(P0.05). There are no significant differences in the activities of soil urease and acid phosphatase between the rhizosphere of tomato and tillered onion. 2) In the intercropping, the contents of soil available nitrogen, phosphorus, potassium and manganese in the tomato rhizosphere are decreased significantly(P0.05), the soil available phosphorus and available manganese in the rhizosphere of tillered onion are decreased significantly(P0.05), and soil pH and organic matter of rhizosphere soil of tomato and available nitrogen, available potassium pH and organic matter of rhizosphere soil tillered of onion have no significant differences, compared to those of the monocropping. 3) Compared with corresponding mono-culture, the P and Mn contents in tomato and the N and Mn contents in tillered onion are increased significantly(P0.05), not in other nutrients in the intercropping. 4) The tomato gray mold disease index in the intercropping is significantly decreased, and significantly and negatively correlated with plant Mn content(P0.05), significantly and positively correlated with plant N/K and N/Mn ratios(P0.01). 【Conclusions】 The intercropping improves the growth of tomato but restrains that of tillered onion. The phosphorus and manganese contents are increased significantly(P0.05), and the N/K and N/Mn ratios in tomato plants are decreased significantly(P0.05) in the intercropping. The tomato gray mold disease index in the intercropping is significantly decreased by the monocropping(P0.05). So the tomato-tillered onion intercropping is an effective way for promoting tomatos healthy growth.