The three-dimensional (3D) Dirac semimetal material of ZrTe5 provides a possible platform for studying 3D Dirac fermions. It can realize both the point-node semimetal phase and line-node semimetal phase when the intrinsic Zeeman interaction acts along different crystalline directions. In this work we present a study of magneto-optical conductivity in ZrTe5. We calculate the optical conductivities in different phases, which exhibit a series of resonant peaks lying on a growing background whose origins are explored. For the Weyl semimetal phase, two striking signatures are found, one is the existence of an additional n = 0 LL transition and another is the double-strong peak structure related to the LL transition in one dispersion branch. While in the line-node semimetal phase, the weak peak appear and the strong peaks have higher degeneracy. We discuss the implications of these results in experiment.