Abstract: The steam generator blowdown system（TTB） of HPR 1000 achieves the requirement of assuming safety functions by adding the accident discharge line to the blowdown line inside the containment to adjust the water level and pressure of the damaged steam generator in the SGTR accident. But how to verify the discharge capacity of the accident discharge line is a problem in the commissioning stage. The structural characteristics of the steam generator is analyzed in this paper, the starting and ending points of the liquid level in the test discharge process are determined. The corresponding relationship between the discharge liquid level difference and the discharge flow rate is studied, the comprehensive error analysis of the test results is performed after calculating the discharge flow, the test result of the accidental discharge line is finally verified to meet the requirements of the safety guidelines. The accident discharge pipeline test of the steam generator blowdown system studied in this paper has a good reference and guiding significance for the commissioning of other nuclear power plants.