Abstract: Polyimide (PI) light-trapping microstructures have shown great potential in improving the performance of optoelectronic devices. However, its high viscosity characteristic makes it difficult to achieve high-precision and large-area forming by traditional micro-nano fabrication techniques. Especially for the high aspect ratio light-trapping structure, the existing ultraviolet (UV) curing imprinting faces the key challenges of incomplete structure filling and insufficient morphology fidelity. Therefore, the study develops a simulation model incorporating two-phase flow of PI resin during imprint filling, revealing the influence of imprinting time, resin viscosity, and imprinting velocity on the filling completeness of microstructures. The experiments of UV curing imprinting replicated PI micro-pyramid array successfully with 500 μm height and 75° inclination angle. Through simulation guides optimization of imprinting parameters (imprinting temperature, imprinting force, and imprinting time), the large-area replication of PI micro-pyramid array achieves 96.2% structural height fidelity with inclination angle deviations below ± 1°. Optical performance testing indicates that the presence of the light-trapping microstructures reduces the surface reflectance of polyimide in the visible range from 7%-12 % to 6%-10 %. Furthermore, the reflectance can be lowered below 1% through the deposition of a coating on the surface of these light-trapping microstructures. The research not only overcomes the challenges in the fabrication of high-aspect-ratio PI microstructures but also provides a reliable and efficient method for the mass production of PI-based light-trapping structures. It offers new insights into the application of PI in advanced optoelectronic devices, promoting the development of high-performance and cost-effective photonic components.