The question as to the state of hydrogen on metallic iron catalyst in ammonia synthesis has been discussed. Charge distribution and energy level diagram of FeH have been calculated by SCCC-LCAO-MO method,the value of negative charge on hydrogen is found to be 0.199. According to the source of hyrogen involved in the process,the synthesis of ammonia from nitrogen may be classified into two groups.In the first group,ammonia or hydrazine is formed by hydrolysis of active dinitrogen complez of low valent transition metal,protonio solvent of the solution being the souxce of hydrogen. In the other group,hydrogen gas sots both as a reducing agent and as a source of hydrogen,and in this process H^6- plays an important role.