The impact of a geocomposite (geotextile casing filled with compacted crushed stone-soil mix) on a railway subgrade is studied using numerical analysis. A finite element model of a single-track railway subgrade has been developed. The stress-strain condition of finite element models was determined. A numerical analysis was performed for a subgrade design option that included a 20 cm protective sand layer below the ballast prism, and a geocomposite (average elastic modulus of 150 MPa, 200 MPa, 250 MPa) under the crushed stone layer. Results indicate that maximum horizontal displacements decrease by a factor of 1.29…1.45 following geocomposite reinforcement, while maximum vertical displacements decrease by a factor of 1.5…1.73. The calculation results proved that the maximum horizontal stresses after the geocomposite reinforcement are reduced by a factor of 1.05…1.14, and the maximum vertical stresses are reduced by a factor of 1.2…1.3. The conducted research proved the effectiveness of using geocomposite as reinforcement for railway subgrade.