Based on full-scale field trials, this study investigated the mechanical properties of geocell-reinforced asphalt pavements. The field site is a four-lane highway in Hubei province in China. The dynamic load tests were performed for the geocell-reinforced and unreinforced pavement under three different conditions of axle loads and running speeds. The static load tests were carried out under three different axle loads which were the same as the dynamic load tests. The dynamic and static responses were studied in relation to the peak of the longitudinal strain, creep strain, and the improvement factors. Field trial results revealed that the longitudinal strain peak value of the pavement structure reinforced by Polypropylene geocell was significantly reduced in comparison with the pavement response without geocell. In addition, the reinforcement system had a certain inhibiting effect on the creep strain and the improvement factor increased with increasing axle load and decreased with increasing speed. Under 100 kN axle load, the improvement factors were 0.78, 0.68, 0.54, and 0.39 at speeds of 0, 20, 40, and 60 km/h. Under 150 kN axle load, the improvement factors were 0.96, 0.89, 0.75, and 0.61 at speeds of 0, 20, 40, and 60 km/h. Under 200 kN axle load, the improvement factors are 1.21, 1.1, 0.97, and 0.79 at speeds of 0, 20, 40, and 60 km/h. This research helps to provide a new and effective method of asphalt pavement reinforcement.