Abstract: Parallel strand bamboo(PSB)fabricated through industrial process using raw bamboo is a high strength bamboo-based composite, and it has extensively potential prospective use as a structural material for building construction. To study the longitudinal stress-strain relationships of this material is a fundamental work to build the constitutive relation of PSB and to conduct the inelastic analysis for PSB structural members. For this reason, this paper investigated the failure mode of tension and compression of PSB in longitudinal direction firstly by test, and then the damage mechanisms of this material were studied. Finally, the analytical stress-strain formula of PSB composite was suggested. The results showed that parallel-to-grain tensile failure of PSB composite was due to the breaking of longitudinal fibers and shown brittle characteristics. The compressive failure was contributed to the bulking of the fibers near the damage area, which has 3 types of failure modes including, longitudinal bulking failure, compressive-shearing failure, and slip failure in longitudinal direction. The stress-strain relationship in longitudinal direction of PSB composite exhibits linear behavior in tension; and in compression. It remains in linear form within the proportional limit, and it can also be simulated by quadratic polynomial, even the stress exceeds the limit.