Abstract: Heat-curable epoxy-resin systems of E44 and E51 were used in tensile properties test of different kinds of carbon fibers according to GB/T 3362-2005. The results show that when the testing conditions of specimen preparation and tensile test were regular, such as sizing type, sizing concentration, curing temperature, curing tension, sizing content of the carbon fibers, speed of loading and strain limit, the tensile properties of carbon fibers still fluctuated within some limits. It was because of the complicated preparation process of carbon fibers. When curing time was not less than 30 min and the resin had cured completely, the kinds of epoxy-resin system and curing time were thought to be less affected the performance evaluation. The data of two common epoxy-resin systems had certain comparability. The carbon fibers multifilament is brittle material, and it is perfectly rational on basis of Hooke’s law that the elongation at break was determined by calculation from the tensile strength and tensile modulus gotten directly by the tensile test.