The invention discloses hot press molding process and device for an aramid paper-based composite material. The process comprises the steps of base material selection, pulping dispersion, compression molding, hot-pressing pretreatment, hot-pressing molding and the like. In the hot-pressing pretreatment step, the obtained primarily-formed aramid fiber paper is extended by using an extension device,so that the outer side of the primarily-formed aramid fiber paper is uniformly distributed. The invention discloses a hot press molding process and device for an aramid paper-based composite material.The extension device has the effect of compressing and extending the dried aramid fiber paper with humidity, so that the aramid fiber paper is effectively adjusted and formed, and meanwhile, the thinner part of the surface of the aramid fiber paper can be effectively filled with the thicker part of the surface of the aramid fiber paper; therefore, the effect of uniformly extending the surface ofthe mixed aramid fiber paper is achieved, and the hot press molding efficiency of the aramid fiber paper is further improved.