The surface structure of InP(111)A has been investigated using reflection high-energy electron diffraction (RHEED) rocking curves and first-principles calculations. We used Ar ion sputtering and low-temperature annealing at about 200 °C as a cleaning method, which yields a (1 × 1) surface structure. RHEED rocking curves reveal that the interatomic distance of the top surface bilayer is compressive. First-principles calculations were performed based on a (2 × 2) unit mesh to obtain a stable structure. The calculated results suggest that a surface compressive bilayer is necessary when In atoms are removed from the surface. We conclude that the InP(111)A-(1 × 1) surface structure comprises about 20%-40% In defects, which exist randomly on the surface, and the compressed surface bilayer has an interval of 0.1 Å.