Abstract: The structural soil strength has always been an important issue in the soil and rock research. The soil and rock is structurally complicated, with a particle chain structure formed by the interconnection of soil particles as one of the dominant morphologies. The analysis for the formation conditions of the particle chain structure of a general type and a friction type is made through building a soil particle chain model, which is used to obtain the conditions for the friction-type particle chain to become stable. On this basis, we attempt to work out soil strength theory for a stable particle chain. It is found from the analysis that the conditions for friction-type soil particles to form a stable chain are related to the fabric relationship of particle composition and also to particle morphology; the strength of a particle chain can influence the soil macro-strength; the length, density and directional distribution of stable particle chains in the soil are important factors for soil strength and also important parameters to characterize the above-mentioned soil structure. The nature of friction-type particle materials to withstand the load is revealed from a particular perspective based on this soil strength theory for a stable particle chain.