Abstract: The low temperature nuclear heating reactor (NHR), developed by Institute of Nuclear and New Energy Technology of Tsinghua University, is highly safe because of its natural circulation at full power level. The driving force of natural circulation is very low, so the flow rate is highly affected by the resistance of the reactor coolant loop. As a result, reducing the flow resistance is a key technology of NHR design. A experiment equipment, which simulated the natural circulation of the reactor coolant loop, was constructed to validate the design. The pressure drop was measured by differential pressure transmitters. The temperature difference of the water in different impulse tubes introduced density difference, which led to large measurement error. Considering the high precision of IAPWS-97, an ActiveX control was developed based on IAPWS-97 to calculate the density of water at deferent pressures and temperatures. The control was used in the data acquisition system based on configuration software platform and the online correction of differential pressure measurement was realized. The testing data analysis shows that the precision of the corrected differential pressure measurement results is highly improved.