Abstract: The concept of subdirect sum of square matrices is extended to tensors according to the relation between matrix and tensor. The definitions of subdirect sum of tensors and S-strictly diagonally dominant tensors are given. It is proved, with the method of classification, that the subdirect sum of two strictly diagonally dominant tensors is also a strictly diagonally dominant tensor. Moreover, the condition ensuring that the subdirect sum of two tensors is the S-strictly diagonally dominant tensor is also given.