Abstract: The high-temperature mechanical properties of carbon fiber reinforced polyimide resin matrix composites MT300/KH420 were studied, during which the tensile and interlaminar shear performance variation rule of MT300/KH420 laminates with[0°]₇, [0°]₁₄ and [±45°/0°/90°/+45°/0°₂]_s fiber orientations were especially analyzed at temperature ranging from ambient temperature to 500 ℃. Results show that tensile strength of [0°]₇ laminate shows an increase while tensile modulus changes little with the increase of temperature until 350 ℃. At 420 ℃ tensile strength and modulus reduce significantly, and at 500 ℃, 65% and 83% of their pristine values remain, exhibiting an excellent high-temperature tensile property. As temperature rises, interlaminar shear strength of MT300/KH420 laminates with[0°]₁₄ degrades continuously from ambient temperature to 420 ℃ where a retention rate of 52.8% is observed. A viscoelastic effect occurs at high temperature, especially at 420 ℃ it turns to be the most severest. Compared with unidirectional laminates, [±45°/0°/90°/+45°/0°₂]_s multidirectional laminates show more stable high-temperature mechanical properties. Mechanical properties of fiber-dominated longitudinal specimen are less dependent on temperature.