In this paper, the experimental research on high-efficiency ortho-para (O-P) hydrogen conversion is carried out. By designing and building a low-temperature O-P hydrogen conversion experimental device, the low-temperature catalytic conversion and pressure drop flow characteristics are studied. The experimental data show that under the same conditions, the catalytic performance of iron hydroxide is the best among the three iron-based catalysts, and the hydrogen flow rate is an important factor affecting the conversion efficiency. The pressure drop formula for the porous region filled with catalyst suitable for the experimental device is proposed. This study has reference significance for the design of high-efficiency O-P hydrogen converter and the optimization design of hydrogen liquefaction process.