A new Hilbert-Huang transform (HHT)-based method for nondestructive instrument structure health monitoring is developed. When applied to bridges, this new method depends on a transient test load and simple data collection. The essense of the method is the newly developed HHT for nonstationary and nonlinear time series analysis, which consists of the empirical mode decomposition and Hilbert spectral analysis. The final decision on the health of the bridge structure is based on two criteria. The first criterion detects the nonlinear characteristic of the intra-wave frequency modulations of the bridge response, which usually appears during comparisons of light with heavy loads. The second criterion detects the frequency downshift as an indication of structural yield. This new method enjoys many advantages: no a priori data required, simple data collection, minimum traffic disruption, and precise and nuance quantitative answers. The result of a case study is presented, which establishes the feasibility of this new approach for structural health monitoring.