Unbonded flexible pipe is widely used in the oil and gas industry for its good flexibility, especially in deepwater oil and gas transportation. And the fiber reinforced unbonded flexible pipe has excellent corrosion resistance and wear resistance. However, they are subjected to internal pressure, external pressure and tensile loads during the service process, which are important factors affecting the integrity and security of the flexible pipe. In this paper, the mechanical behaviors of an 8-inchs fiber reinforced unbonded flexible pipe used in offshore gas development which consists of internal layer, internal pressure reinforcement layers, anti-wear layers, external pressure armor, tensile reinforcement layers and outer sheath is investigated by numerical methods. A rigorous three-dimensional solid finite element model of flexible pipe that considers the real material parameters, structural nonlinearity as well as the nonlinear contact behavior was created. ABAQUS/Explicit quasi-static simulation is adopted to study the mechanical behaviors of the flexible pipe under combined load. And the accuracy of the simulation method for the fiber reinforced layers such as internal pressure layer is verified by comparing with the small-scale internal pressure burst test of 1-inch flexible pipe. The mechanical behavior of flexible pipe subjected to internal pressure, external pressure and tensile load was investigated in detail. Based on the contrastive analysis, some practical conclusions have been obtained which may be used for the practical design and production of flexible pipe. This study can be referenced for the applications of unbonded flexible pipe in marine oil and gas production.