Abstract: Once through steam generator (OTSG), with its advantage of compact structure and high power density, is widely used in petroleum and chemical industry, thermal power generation, and other industrial fields, and especially plays a vital role in integrated modular nuclear reactor. The narrow-channel heat transfer technology with double side heating is adopted in the doublepipe OTSG, which effectively reduces the thermal resistance of heat conduction and has higher heat transfer efficiency than the straight tube OTSG. In order to study the influence of the parameters under different operating conditions on the steam temperature of the double-pipe OTSG, a dual loop steam generator thermal-hydraulic characteristics test bench with high-temperature and high-pressure heat transfer medium in the primary side and low-temperature and low-pressure working medium in the secondary side was built. The flow diagram of test circuit, the scale and internal structure of the heat transfer tube of the test section, the setting of the experimental working condition range, and the experimental method were introduced in detail, and the uncertainty of the measured data was finally analyzed. The single variable method was used to study the influence of different parameters (average temperature of the primary circuit, load, steam pressure and feedwater temperature) on steam temperature under steadystate conditions, that is, the sensitivity analysis of operating parameters on steam temperature. The average temperature range of the primary circuit is from 282 ℃ to 307 ℃. The load range is from 20%FP to 120%FP. The steam pressure range is from 4.0 MPa to 6.0 MPa. The feed water temperature is between 40 ℃ and 160 ℃. The experimental results show that the lower the average temperature of the primary circuit is, the lower the steam temperature is. The closer to the saturation temperature of steam temperature, the greater drop is produced in steam temperature. The steam pressure has no effect on steam temperature under low load (20%FP-60%FP). However, the steam temperature decreases with the increase of steam pressure under high load (60%FP-120%FP), and the drop rate continues to increase. With the increase of load, there is a maximum steam temperature point. When the steam temperature is less than the peak value, the steam temperature rises slowly with the load. Conversely, when the steam temperature is greater than the peak value, the steam temperature drops sharply with the load. As for the influence of steam pressure, when the steam pressure increases, the peak value of steam temperature decreases. Accordingly, the load at the maximum steam temperature point also decreases. With the increase of feedwater temperature, the steam temperature decreases, but the reduction rate is very small compared with other parameters.