The ortho-para H_2 catalytic conversion equipment has been developed to reduce the evaporation loss from stored liquid hydrogen. The ortho-para H_2 conversion heat is evaluated at liquid nitrogen temperature. This problem is of particular interest in the design of the ortho-para H_2 conversion equipment consists of a catalytic converter, a precooler, and a liquid nitrogen bath. 30-90 cc of Fe(OH)_3 are employed as a catalyst in the present converter. The conversion heat and conversion effectiveness are evaluated when mass flow rate of hydrogen is in the range of 0.05-1.6 g/min. It is found that the ortho-para H_2 conversion heat is increased while conversion effectiveness is decreased as the mass flow rate of hydrogen is increased. Both the ortho-para conversion heat and conversion effectiveness are increased with an increase in the amount of the catalyst.