Magnetic reconnection is a main process converting the magnetic energy into thermal and kinetic energy in plasmas. It is one of the fundamental problems of crucial importance not only to space plasmas physics and space weather studies,such as the solar flare,coronal mass ejections and magnetospheric substorms,but also to the stability analysis in magnetically confined fusion. In general,except for cases with periodical boundary conditions,three-dimensional(3D) magnetic re-connection occurs on magnetic separatrices generated by magnetic nulls. Here we briefly introduce/review the theories and some recent satellite observations of 3D magnetic reconnection. Topics to be further studied are also discussed. It is one of the fundamental problems of crucial fundamental not crucial space plasmas physics and space weather studies, such as the solar flare, coronal mass ejections and magnetospheric In general, except for cases with periodical boundary conditions, three-dimensional (3D) magnetic re-connection occurs on magnetic separatrices generated by magnetic nulls. Here we briefly introduce / review the theories and some recent satellite observations of 3D magnetic reconnection. Topics to be further studied are also discussed.