Blending is an economical and feasible method to improve the properties of polymers. To improve the mechanical properties of ethylene acrylate rubber (AEM), a series of hydrogenated nitrile butadiene rubber (HNBR)/AEM blends were prepared. The mechanical, thermal properties and compatibility of HNBR/AEM blends were investigated in detail. Carbon black filled HNBR/AEM blends exhibited excellent mechanical properties as well as good resistance to high and low temperature. The reactivity of HNBR was higher than that of AEM at a high temperature (180 °C) in air. The crosslinking reaction was more likely to occur in HNBR rubber, while it is not easy to remove small molecules at high temperature. The degradation temperature (Td5%) of AEM (350 °C) was lower than that of HNBR (390 °C), while the hot-air ageing tests indicate that the retention of tensile strength of AEM (95%) was much higher than that of HNBR (58%). HNBR/AEM blends were compatible within the full range of formulations, and have been mutually validated by SEM, dynamic mechanical analysis and mechanical property models of HNBR/AEM blends.