Full-waveform inversion is the core technology for achieving high-precision velocity modeling at present. However, in areas with steep structures, complex wavefield propagation characteristics and strong lateral velocity variations often lead to poor convergence of the inversion process and reduced model accuracy. Crosswell seismic data, owing to their unique acquisition geometry and high signal-to-noise ratio, provide a reliable data basis for high-steep structural imaging. Therefore, this study proposes a high-precision full-waveform inversion method based on crosswell seismic data. Firstly, crosswell seismic forward modeling technology was employed to simulate the theoretical model of high-steep structures and generate synthetic data, construct the residual error between the simulated and measured data, and establish an L₂-norm objective function based on this residual error. On this basis, the gradient of the objective function was efficiently computed by the adjoint-state method and combined with the limited-memory Broyden–Fletcher–Goldfarb–Shanno optimization algorithm to iteratively update the velocity model based on the gradient, thus effectively reducing the risk of convergence to local extrema and improving the convergence and stability of the inversion process. Numerical simulation and field data processing results show that this method effectively delineates the boundary details of steep structures and improves the resolution of the velocity model, providing strong technical support for fine exploration and efficient development of complex structural oil and gas reservoirs.