Organic-inorganic halide perovskite materials are widely used in solar cells because of their excellent photoelectric properties. However, the stability and lead toxicity issues associated with materials and devices have limited their production and development. Compared with the hybrid perovskite, the inorganic lead-free perovskite Cs3Bi2I9 has attracted wide attention because of its stronger stability and environmental friendliness. Cs3Bi2I9 has three crystal types: monoclinic, trigonal and hexagonal. At present, researches on Cs3Bi2I9 are mainly focus on the hexagonal phase. In this paper, based on the first principles of density functional theory, the electronic properties, carrier effective mass, stability, and optical properties of Cs3Bi2I9 monoclinic, trigonal, and hexagonal phases are studied theoretically. It is suggested that the stability of the three crystal phases are similarity, and the direct band gap (1.21 eV) of the trigonal phase would be noteworthiness. For the three phases, the effective mass showed the same properties along the a and b directions and different along the c direction. The effective mass of electron of the trigonal phase is significantly smaller and along the a-direction is smaller than that of c-direction. Corresponding to the red shift phenomenon of optical properties, the trigonal phase shows the better optical absorption performance than that of others. In addition, the optical properties also show the same properties along the a and b directions and different along the c direction, and the optical absorption performance along the a-direction is better than that of c-direction.