Abstract <p>Fiber-reinforced cemented soil (F-RCS) is an artificial multiscale geo-material, the strength of which is determined by the physical and mechanical properties of various substances of the F-RCS. To study the effect of fiber content and fiber length on the shear strength of the F-RCS, the substance phases of the F-RCS are divided into reinforcement fiber and cemented soil matrix to establish a meso cell structure of the F-RCS, which can reflect the internal substance properties of the F‑RCS. Moreover, according to microscopic kinetic characteristics of reinforcement fiber and cemented soil matrix and the mesoscopic strain gradient theory, a multiscale Mohr-Coulomb strength criterion (MCSC) of the F-RCS is deduced, and its yield locus is drawn on the π plane. Furthermore, consolidated and undrained triaxial compression tests are conducted on the F-RCS samples with various fibre content and fibre length to obtain the model parameters, and verify the proposed multiscale MCSC of the F-RCS. Results show that the multiscale MCSC the F-RCS is capabel of effectively predicting the shear strength of the F-RCS. The shape of the yield locus of the MCSC of the F-RCS is hexagonal and expands with increasing fiber content and fiber length. The shear stress of the F-RCS predicted by the multiscale MCSC of the F-RCS showcases good agreement with the test results.</p>