## 1 Introduction
Although the traditional flame-retardants are obvious in the flame retardant effect on CF/EP composites, it is a fact that the mechanical properties would be weakened which are not exhibited in the research. To solve this, some nano-flame-retardants were incorporated in the CFRP system which was expected to improve both of the flame retardancy and mechanical properties. [PERSON] et al. prepared MWCNT/GNP membranes reinforced CFRP composites and the results showed that the incorporation of the hierarchical MWCNT/GNP membrane with 7.5 wt % of GNP displayed a 35% reduction in the peak heat release rate (PHRR) for a CFRP composite plate with the epoxy as matrix and an 11% reduction in PHRR [15]. [PERSON] et al. found composites containing 0.4 wt % MWCNTs showed a 9.6% increase in erosion resistance compared with the carbon fiber epoxy matrix composites, and thermal conductivity increased 52% with the addition of 0.4 wt % MWCNTs [16]. [PERSON] et al. prepared MMT and APP modified GF/EP/CNTs composites to enhance its flame retardant properties, and the results showed that the combination of 0.5 wt % CNTs with 5 wt % MMT can increase the initial thermal decomposition temperature up to 62 \({}^{\circ}\)C; the addition of APP and CNTs together could increase LOI about 8% [17]. [PERSON] et al. incorporated CNT buckypaper and CNF paper to CFRP, and the results showed that MWCNT buckypaper acted as an effective flame-retardant shield, reducing the peak heat release rate by more than 60% and reducing smoke generation by 50% during combustion [18]. [PERSON] et al. prepared different flame retardants reinforcing the CFRP and results showed that with selective flame retardants (FRs), the FR chemicals decreased the flammability of composites up to 50% without affecting their mechanical properties [19]. [PERSON] et al. prepared the fabrication of an epoxy adhesive system incorporated with an aligned MWCNT and VGCF and found that a remarkable 370% increase in Tc was observed for the combined effect of 3 wt % of the aligned MWCNT with a VGCF filled epoxy adhesive system [20]. [PERSON] et al. found glass transition temperature and CTE (Coefficient of thermal expansion) of the CFRP was reduced by the addition of MWCNTs, whereas MWCNT-CFRP was found thermally stable up to 350 \({}^{\circ}\)C [21]. [PERSON] et al. constructed the flame retardant coating rapidly on the surface of the carbon fiber, which was used as the reinforcement to modify EP, and the results showed that when the content is 4.5 wt %, the oxygen index of the composite is 39% and can pass the vertical combustion V-0 level [22]. At present, the research on the three-phase composites mainly focuses on the preparation method, mechanical properties, thermal properties, and electrical properties. However, the fire performance of the polymer composites is essential to ensure the intrinsic safety to widen its use in more fields. There are some studies to investigate the flame-retardant properties of the traditional and nano flame-retardants to modify the CFRP composites as described above. However, what we did in this paper was to investigate the flame retardant properties of the multi-walled CNTs-OH reinforced short-CF/EP composites. In addition, there are not enough studies to report this issue and it deserves to be systematically investigated in order to understand the nature of the composites. In this paper, CF/EP composites and CNTs/CF/EP composites were prepared by solution blending respectively. The flame retardancy and thermal stability were studied by cone calorimetric test and thermogravimetric analysis respectively. The influence of the reinforcement on its mechanical properties was studied by tensile and flexural tests.