Based on the density functional theory and nonequilibrium Green's function method, we investigate the electronic structures and thermal spin transport properties of Christmas-tree silicene nanoribbons (CSiNRs). The results show that CSiNRs have ferromagnetic ground state with high Curie temperature far above the room temperature. Obvious spin Seebeck effect with spin-up and spin-down currents flowing in opposite directions by a temperature gradient can be observed in these systems. Furthermore, a thermal colossal magnetoresistance up to 10(9)% can be realized by tuning the external magnetic field. The results show that CSiNRs hold great potential in designing spin caloritronic devices. (C) 2018 Elsevier B.V. All rights reserved.