THz time domain spectroscopy (TDS) with picosecond temporal resolution is employed to investigate the spin coherence in a canted antiferromagnetic RFeO3 with R rare-earth ion. The magnetic component of incident THz pulse can be coupled effectively with the ferromagnetic (FM) and antiferromagnetic (AFM) modes of the crystal which leads to the excitation of the two kinds of modes of spin waves. In this talk, by employing TDS technique, we will focus on the dynamical spin reorientation transition in NdFeO3 crystal triggered with temperature and external magnetic field. Our studies reveal that the spin reorientation transition triggered by external magnetic field is strongly anisotropic: magnetic field along a-axis is much easier to switch the spin alignment than that along c-axis in NdFeO3 crystal. Our results demonstrated that THz spectroscopy is a sensitive way to study the spin reorientation, and which also shed light on THz switching of spin reorientation dynamics in this canted antiferromagnetic structures.