This paper deals with the class of Q-tensors, that is, a Q-tensor is a real tensor A such that the tensor complementarity problem(q, A):finding an x ∈ R~n such that x ≥ 0, q+Ax~(m-1)≥ 0, and x~T(q+Ax~(m-1)) = 0,has a solution for each vector q ∈ R~n. Several subclasses of Q-tensors are given: P-tensors, R-tensors, strictly semi-positive tensors and semi-positive R_0-tensors. We prove that a nonnegative tensor is a Q-tensor if and only if all of its principal diagonal entries are positive, and so the equivalence of Q-tensor,R-tensors, strictly semi-positive tensors was showed if they are nonnegative tensors. We also show that a tensor is an R_0-tensor if and only if the tensor complementarity problem(0, A) has no non-zero vector solution, and a tensor is a R-tensor if and only if it is an R_0-tensor and the tensor complementarity problem(e, A) has no non-zero vector solution, where e =(1, 1 ···, 1)~T.