Abstract: Abstract: In recent years, there has been increasing interest in the use of natural fiber reinforced polymer in many fields due to low density, high specific strength and eco-friendly property. However, the application of composites is faced with difficulties in outdoor environment, such as water absorption, degradation, low mechanic strength and dimensional stability. In order to improve the aging-resistant property of flax fiber fabrics/basalt fiber fabrics reinforced UP (unsaturated polyester resin), the author used the artificial simulating climate box (ultraviolet and condensation) to accelerate ageing process of HCM (hybrid composite materials), which was composed of different sandwich layers and included H1, H2 and H3 representing basalt fiber content of total fibers of 20.3%, 41.5% and 63.7%, respectively. Mechanical properties, DMA (dynamic mechanical analysis) performance and microstructure of HCM were affected by basalt fiber content and aging time. The result showed that both flexural strength and impact strength first increased and then decreased with aging time. The retention of flexural strength was 62.5%, 58.1% and 57.0% for H1, H2 and H3, respectively. With regard to impact strength, the figures were 66.8%, 66.7% and 53.2% for H1, H2 and H3, respectively. The results of ANOVA (analysis of variance) and LSD (least-significant difference) illustrated that ultraviolet aging time had significant effects on flexural strength of H3 (P<0.05) while basalt fiber content had not significant effects on flexural strength retention (P>0.05). As ultraviolet aging time increased, rigidity and frangibility of HCM increased gradually. The poor interfacial adhesion was demonstrated between flax fiber and UP by DMA. The result of SEM (scan electron microscope) indicated a poor interfacial adhesion between flax and UP matrix, such as debonding and more voids. However, basalt fibers and UP matrix were combined closely and matrix fragments around basalt fibers were found. The main reason was that hydrogen bond produced after absorbing water destroyed the interface between flax fibers and UP matrix. So process of water damage in the interface was verified by SEM. In conclusion, mechanical properties of HCM increase slightly owing to further solidified substrate. However, with the extension of aging time, irreversible hardening happens to matrix, followed by micro-crack appearing between fiber and matrix, which leads to a decrease in mechanical properties of HCM. In addition, water has significant effect on flax fiber and the mechanism of water damage is approved by SEM results. The manufacture of HCM by using natural degradable fibers is meaningful to environmental protection; on top of that, it can provide the reference to aging-resistance improvement of inorganic fibers/plant fibers reinforced polymer HCM.