Abstract: Time and space are two absolute concepts that are independent but closely related to each other, and are two basic dimensions on which all things exist in the world. Truth has the two dimensions, and changes concretely. Out of time and space, truth loses its dimensions of moving and changing, and inevitably loses its character of correctly reflecting things and their laws. From the perspective of space-time transformation, the value of truth in different space-time situations is analyzed, so as to understand truth in a more comprehensive and in-depth way.