The influence line (IL) of bridges plays a critical role in assessing bridge health conditions and behavior. However, in engineering, due to the dynamic fluctuations caused by vehicle-bridge interaction and road roughness, the IL cannot be obtained directly from bridge responses. This paper proposes a rapid method for identifying bridge IL using structural dynamic responses from two vehicular passages. Initially, analytical solutions for the IL of a simply supported bridge are presented. To address dynamic fluctuations, empirical mode decomposition is utilized to decompose bridge responses into intrinsic mode functions (IMFs) to approximate quasi-static response. Subsequently, the equations based on residual bridge responses induced by forward and reverse passages, which can automatically remove the scale error of IMFs, are introduced to calculate the bridge’s IL at discrete points. Furthermore, cubic spline interpolation, combined with boundary conditions, is used to obtain the complete IL of the bridge. Numerical simulations, incorporating interaction between a two-axle vehicle and a simply supported bridge, along with road roughness, are conducted to verify the effectiveness of the proposed method. Results show a close match between identified IL and analytical results, particularly for smooth or Class A road roughness.