In this study, cv. MoneyMaker (Solanum lycopersicum L.) wild type and MoneyMaker backgrounded phytochrome B1 mutant (phyB1) were used as the materials. The changes of seedling root morphology indexes, osmotic regulation substance contents, active oxygen species content, antioxidant enzyme activities, MDA content and relative electrolyte permeability in leaf and root under salt stress (100 mmol·L-1 NaCl) were analyzed at the light environment that red light to far red light ratios (R∶FR) were 7.4, 1.2 and 0.8. The aim was to study the effects of different R∶FR values on oxidation resistance ability of tomato seedlings and the role of phyB1 in these effects. The results show that：（1） Under salt stress, wild type tomato seedlings and phyB1 mutant tomato seedlings significantly decreased root morphology indexes (total root length, total root surface area, number of root tips, number of root forks) compared with CK, significantly increased osmotic regulation substance (soluble protein and proline) contents, active oxygen species (O-·2和H2O2 and H2O2) content, antioxidant enzyme (SOD, POD, CAT) activities, MDA content and relative electrolyte permeability in leaf and root compared with CK.（2）Reducing R∶FR value of growth light environment under salt stress, wild type tomato seedlings significantly increased root morphology indexes, osmotic regulation substance contents, antioxidant enzyme activities in leaf and root compared with seedlings under salt stress, significantly decreased active oxygen species content, MDA content and relative electrolyte permeability in leaf and root compared with seedlings under salt stress, but the indexes mentioned above had no significantly different in phyB1 mutant tomato seedlings among different R∶FR values. This research suggests that the lower R∶FR value promoted wild type tomato root growth, increased osmotic regulation substance contents and antioxidant enzyme activities, decreased active oxygen species content in leaf and root, MDA content and relative electrolyte permeability in leaf and root, so that improved the oxidation resistance ability of wild type tomato, promoted the growth of tomato, when R∶FR value was 0.8 the improvement effects of oxidation resistance ability was the best; and phyB1 play an important role in lower R∶FR value improving oxidation resistance ability of tomato.