Erbium-doped lithium niobate thin films offer a promising optoelectronic platform by combining the gain performance with the electro-optic and nonlinear properties of lithium niobate, potentially enabling single-chip full integration. This study aims to develop an integrated waveguide amplifier based on erbium-doped lithium niobate thin films to meet the growing demand for compact and efficient optical amplifiers in optical communication networks. This study explores on-chip gain theory and conduct experimental validation. A lithium niobate waveguide with a propagation loss as low as 0.18 dB/cm was prepared by combining electron beam lithography with dry etching. Employing a 1484-nm bidirectional pumping scheme, a 10-cm-long integrated waveguide amplifier demonstrated a signal enhancement of 62.76 dB and a net gain of 22.26 dB. The experimental characterization results closely align with the gain simulation outcomes. This research provides a critical experimental basis and theoretical support for further optimizing integrated optical amplifiers based on erbium-doped lithium niobate thin films and broadening their applications in optical communication.