The analysis of current development of atomic frequency standards is given on the basis of hydrogen masers. The report contains the analysis of basic destabilizing factors limiting frequency stability of active and passive hydrogen masers. The paper describes design solutions of active and passive hydrogen masers insuring high short-term and long-term frequency stability. Today，the values of -1.10-13 second and 3.5.10-16 per day for active hydrogen maser,and of 4.10-13 one second and 2.5.10-15 per day for passive hydrogen maser are achieved. The further improvements of performance specifications of hydrogen masers are discussed.