Abstract: 【Objective】To explore the effects of different bio-priming conditions on seed vigor and seedling physiological characteristics of tomato under low temperature stress,and to provide a feasible scheme for the future out-ofseason open-air cultivation of tomato.【Method】With tomato seed Zhongduhongyun was used as material,Trichoderma harziensis and Pseudomonas fluorescens were used as seed priming agents,and five treatments were set up:which were non-primed treatment(CK),1×10⁷ CFU/m L spore fluid(T1) and fermentation fluid(T2) of T.harziensis and P.fluorescens,1×10⁶ CFU/m L fermentation fluid(T3) and sterile filtrate(T4).The germination index of seed was measured after drying.4℃low temperature treatment was set for seedings,normal condition(25℃)was control,the morphology indexes and physiological indexes were detected.【Result】The four priming treatments promoted seed germination and plant growth in different degrees,and the promotion effect was significant.According to the seed germination index,the priming effect was T4>T3>T2>T1,significantly increased by 90.00%,67.70%,51.30%,50.00%in terms of vitality index,respectively.After 60 d of seedling morphology indexes analysis,it was found that the plant height,stem diameter and stem fresh weight of T4 reached the maximum value,while the root length and stem fresh weight of T2 reached the maximum value.Analysis of physiological indexes of 60 d seedlings showed that the catalase(CAT) content of T2 was the highest.The content of photosynthetic pigment and soluble sugar showed the order of T4>T3>T2>T1,and the contents of soluble protein and proline(PRO) in T4 reached the maximum value,significantly increasing by 71.74%and 46.50%,while the increase of other treatments was slightly lower than that of T4.The relative conductivity(REC) of T1,T2,T3and T4 changed little before and after low temperature stress,while CK increased sharply after low temperature stress.The increment of MDA content after low temperature stress was T3>T4>T2>T1.Correlation analysis showed that plant height,stem diameter and stem fresh weight were extremely significantly positively correlated with plant CAT content(P<0.01,the same below),root fresh weight was extremely significantly negatively correlated with REC and MDA content,and extremely significantly positively correlated with PRO content.【Conclusion】Equal volume mixing sterile filtrate of T.harziensis and P.fluorescens priming tomato seeds can improve seed vitality,promote plant growth,increase the protective enzyme activity in plants,and thus improve the low temperature tolerance of tomato plants.