Abstract: From the standard model(SM) in particle physics,the mass of a photon is considered zero,mγ=0,which has universally been accepted.The unified theory of weak and electromagnetic interactions is expressed in the symmetry groups SUL(2) Ue(1),and if mγ≠0,the symmetry of Ue(1) must be destroyed.There are indications that the rest mass of a photon isn’t zero,namely mγ≠0,in some recent theoretic researches and experiments.If the rest mass of a photon is really not zero,the foundation of the standard model will be shaken once again.