The phase behavior of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) triblock copolymers in aqueous solutions is studied by using a self-consistent-field theory. The spectral method is extended to polymer models with internal degrees of freedom. Phase diagrams of PEO-PPO-PEO and PPO-PEO-PPO triblock copolymers in water are constructed in the concentration-temperature space. A variety of lyotropic liquid crystalline phases is found. The effects of temperature, copolymer concentration, the block (EO/PO) ratio and the chain architecture are investigated. Good agreements were found between experimental results and theory.