To investigate the effects of geogrid embedment length L and sand type on the interface behavior of reinforced soil, a series of pullout tests were systematically conducted based on three key parameters: geogrid embedment length L, normal stressσ_v, and sand type. The peak pullout resistance, soil-geogrid interface strength, strain distribution of the geogrid, and thickness evolution of the reinforced soil influence zone were analyzed under various working conditions, and evolution characteristics of the strength of the reinforcement-soil interface. The results show that the peak pullout resistance is enhanced by increasing L, σ_v, and the average particle size of the sand d₅₀ when the geogrid remains intact. A polynomial regression model is developed to express the peak pullout resistance as a function of L, σ_v, and d₅₀. The apparent cohesion c of the soil-geogrid interface is observed to increase with d₅₀ but decrease with L, whereas the apparent internal friction angle φ is positively correlated with L and minimally affected by d₅₀. Functional relationships between c, φ and L, d₅₀, as well as between the interface friction coefficient f and L, σ_v, d₅₀, are established through multivariate fitting methods. The strain decay rate in the embedded geogrid section is found to decrease gradually with increasing L. The strain reduction proportion from the BC to CD segments is reduced from over 80% at L = 30 cm to 50% ~60% at L = 40 cm. The thickness of the reinforced soil influence zone is shown to increase with σ_v and d₅₀, while L exhibits negligible influence on this thickness.