Taking tomato variety‘stone’as test material，the paper carried out salt stress test on tomato
root system by hydroponic device and wiping out main root and lateral root．Four treatments of salt stress
concentration were 0（CK），0.1%，0.2% and 0.3%，respectively．The paper studied the growth status and
salt tolerance threshold of tomato root system by testing lateral root system activity，dry root weight and root
morphological parameters，etc. indexes．The results showed that the growth of lateral roots all accorded with
the slow-fast-slow Logistic growth model．Stress with 0.1% salt concentration could delay the development
progress of root system．The root system activity，dry root weight and root system morphological parameters
were all higher than that of the contrast．Under stress with 0.2% and 0.3% salt concentration，the root system
development progress was all ahead of schedule，then the dry root weight and root morphological parameters
were all lower than that of the contrast．The growth of root system was inhibited．The injuried main root would
stimulate the survival potential of lateral roots conducting compensatory growth．The root morphological
parameters had bigger contribution to salt tolerance．Total root length，root superficial area and root volume
could be taken as salt tolerance indexes．To sum up，the salt stress environment benificial to lateral root growth
is 0.1% salt concentration．The Logistic model can be used to predict the origin，peak and terminal points of
root growth，so that effective measures can be taken to regulate the growth of lateral root under salt stress．