The steel pony-truss bridge is a structure commonly used in road and rail traffic. It has a simple structure, a large bearing capacity, and high economic efficiency. The safety of steel pony-truss bridges is highly dependent on the stability conditions of the top chord. This paper presents the reliability assessment of the compressive top chord of steel pony truss bridges according to stability conditions. For this purpose, a deterministic model was built from the stability conditions of the compressive top chord; then, a stochastic model was established based on the deterministic model, in which the structural geometries and material properties are random parameters. Finally, the reliability of the structure is evaluated using Hypercube Latin sampling and Monte-Carlo simulation.