Abstract: Some teaching experiences about electrodynamics and special relativity are summarized. Several relativistic

invariants and“Pythagorean theorems”in special relativity are derived by means of the tensor theory in

four - dimensional Minkowski space and the contraction operation rules of these tensors. Meanwhile， some

application examples are given in illustration of these formulae.

Key words: special relativity, tensor, relativistic invariant, Pythagorean theorem, four - dimensional Minkowski space, Lorentz transformation