[Objective] Generally, root is the main organ of a plant to absorb water and nutrients in soil, and how it grows and distributes is an important indicator of a crop in growth and development. The commonly used methods for monitoring crop root growth, such as the soil drilling and excavation methods, are what we call destructive sampling methods. Although they are usually quite high in accuracy, they are not suitable for in situ monitoring of root growth. Therefore, the minirhizotron technique is recommended as an effective method for in-situ monitoring of crop root growth thanks to its rapid and non-destructive approach.[Method] In order to reveal impacts of salt stress on root growth of wheat, a pot culture experiment was conducted, with soil salt content varying along a gradient from 0.61(CK), 1.61(S1), 2.61(S2), 3.61(S3), 4.61 (S4) to 5.61 g·kg^-1 (S5). And the minirhizotron technique was used to- collect digital images of the roots at tillering, reviving, jointing and booting growing stages. Then root length, root length density and their distribution in the soil as affected by salt stress were determined with the aid of the digital image processing technology.[Result] Results show that with the aid of the minirhizotron technique, growth and development progresses of the wheat root in the experiment could be intuitively monitored. In the experiment the root length density obtained with the technique was found to be significantly and positively related with that with the soil drilling method (r=0.91), especially at the jointing and booting stages of the crop. Moreover, comparisons of the root images with the root parameters analysis relative to growing stage of the crop revealed that wheat root distributed mostly in the 0-10 cm soil layer and decreased with soil depth, and that root length decreased with rising soil salt content at all growing stages. For example, at the tillering stage, the root length in treatment S5 (S5, 6.61 g·kg^-1) was less than half of that in CK, and at the booting stage it was only one-third of that in CK, indicating that the wheat root growth was greatly inhibited by salt stress. The worst occurred at the booting stage, especially in the treatments with soil salt content higher than 3 g·kg^-1. It was mainly because high soil salt content caused the root rust and dead, and the higher the soil salt content was, the more obvious this phenomenon was.[Conclusion] Thus, the minirhizotron technique combined with the image processing technique could be used as a more effective method for obtaining root growth parameters as compared with traditional destructive sampling methods. This paper provides a theoretical basis and technical support for in situ monitoring intuitively of crop root growth in saline soils.