To address the capability bottlenecks of multi-line structured light caused by fixed line spacing angle and narrow depth of field, this paper proposes a novel multi-line structured light projection system regulated by liquid lenses and develops a method for adjusting the characteristic parameters of light stripes. Firstly, based on the given system design configuration, a structured light projection parameter model based on dual liquid lenses is established, and a bi-level optimization method for solving structural parameters is formed by combining nonlinear programming and genetic algorithm. Then, to adjust the structured light stripes under varying projection distance, a control strategy for the liquid lens is provided, and a neural network structure is proposed to model the mapping from system parameters to line spacing angles. Finally, a physical prototype of a liquid-lens-controlled variable structured-light projection system is constructed, and a series of experiments are designed and conducted to evaluate system performance and verify the effectiveness of the proposed method. Compared with traditional schemes, this method has the ability to substantially extend the effective projection distance of multi-line structured light (keep the linewidth of light stripes within 1.25 mm). By coordinately regulating the input currents of the dual liquid lenses (without moving components during operation. The system is able to generate dynamically adjustable structured-light fringes with inter-line spacing angles ranging from 0.537° to 0.986°, achieving an angular magnification of up to 1.836. Based on the dataset obtained through calibration, a mapping network model is constructed to relate the dual liquid-lens parameters to the inter-line spacing angle. Experimental evaluation shows that the model achieves an average prediction error of 1.07% for the inter-line spacing angle. These results demonstrate that the proposed system and method can flexibly adjust the density of multi-line structured-light fringes according to factors such as the target′s size and position, while strictly controlling the stripe linewidth. The proposed approach provides a new technical pathway for enhancing the detection performance of multi-line structured-light systems.