In recent years, the electronic equipment and measuring instrument are moving into integration and miniaturization. The sizes of precision structured optical elements have been developed to sub-micron level. For diffractive optical elements, it has a micro scale structure and needs have superior optical performance with very high shape accuracy. For many electronic equipment, the LCP material is used manufacture electronic equipment, because it has high fluidity and dimensional stability. This study aims to investigate the effect of polymers and mold temperature on the micro-structure of off-axial aspherical reflective grating optical element (OAA-RGOE) in injection molding (IM) process. The IM process combines a micro vibratile (MV) and varithermo mold temperature (VMT) methods. In this study, three polymers including liquid crystal polymer (LCP) with polycarbonate (PC) and polyphenylene sulfide (PPS) have been used to make OAA-RGOE to investigate the structured optical elements. Results show that LCP’s surface topography of the micro-structure is much smoother than those made by PC and PPS. The measurement results also present that the micro-structure filling ratio (MSFR) has increased with higher mold temperature. The structure height of OAA-RGOE is around 0.45 µm and MSFR has been achieved around 91.22 % at mold temperature (100 °C). LCP material has provided a high applicability for OAA-RGOE in IM process. This study can be further applied to manufacture micro-structure of reflective optical element by LCP material.