Spontaneous formation of ordered structures from amphiphilic molecules has attracted tremendous attentions in the last decades. Among the many different amphiphilic systems, block copolymers with their rich phase behavior and ordering transitions have become a paradigm for the study of structural self-assembly. For the simplest case of diblock copolymers, which are linear polymers composed of two different sub-chains (A and B blocks), a variety of ordered bulk phases, including lamellae, hexagonally-packed cylinders, body-centered-cubic spheres and a bicontinuous network structure called gyroid, are observed. Understanding the structures and phase transitions in block copolymers has been one of the most active research areas in polymer science in the past two decades. One of the achievements from these efforts is the self-consistent field theory (SCFT), which provides a powerful framework for the study of ordered phase of block copolymers. Due to the complexity of the theory, finding solutions of SCFT for different phases of block copolymers has been a challenge for the last decades. Traditionally, numerical methods in reciprocal-space and in real-space have been developed. Recently we have developed a generic spectral method, which is capable of predicting complex phases of block copolymers. After a brief review of the available method of solving SCFT equations, I will present this recent development of self-consistent field theory for block copolymers and its applications to ABC triblock copolymers.