The first-order magnetic phase transition between antiferromagnetic (AFM) and ferromagnetic (FM) states around room temperature is one of the unique features in FeRh. More fascinating is that the phase-transition temperature can be readily modulated by the magnetic field. In this work, we demonstrate the spin current valve by tuning temperature or magnetic field across the first-order phase transition. The spin-polarized current  driven by the anomalous Nernst effect (ANE) can be readily excited in the FeRh FM state, but completely suppressed in the AFM state. As a result, the colossal magneto-spin polarized voltage in FeRh has been demonstrated, where the ratio of the thermally excited magnonic  associated with the spin conductivity between the FM and AFM states is near infinity during the first-order phase transition. Furthermore, in isothermal conditions, the spin conducting and non-conducting states can be switched by magnetic field, and the critical magnetic field for the on/off switch can be significantly decreased with increasing temperature. With virtually infinite spin current on/off ratio and tunable critical field and temperature, FeRh is significant for spintronic devices.