Abstract: Automatic depressurization system (ADS) is widely used in the third generation of nuclear power plants as an important passive technology to deal with small break loss of coolant accidents. At present, ADS related research has mainly focused on the influence of the AP1000 ADS on the primary loop under a single accident. However, the study of other advanced pressurized water reactor (PWR) ADS and the operational characteristics of the ADS itself under a variety of typical ADS triggering accidents have rarely been discussed. In this paper, the transient thermal hydraulic characteristics of primary loop and ADS operational characteristics under typical accident conditions of Chinese advanced PWR were investigated at different levels by using the system analysis program RELAP5/MOD3.4. According to the specific structural and operational characteristics of Chinese advanced PWR, the analysis model of this plant was established by using RELAP5/MOD3.4. The model mainly included reactor coolant system, secondary loop system, secondary-side passive residual heat removal system, passive safety injection system and ADS of Chinese advanced PWR. Based on the four typical ADS triggering accidents, including 2 inch and 10 inch cold leg break, ADS valve inadvertently opened and double-ended direct vessel injection line break, the effects of ADS on the primary loop pressure, cladding temperature, passive injection flow and sprayer discharge state were studied. The results show that under typical ADS triggering accidents, the step-by-step opening of ADS can make the primary loop pressure gradually reduce to the input pressure of the outside containment tank, so that the three passive water tanks can be injected in an orderly manner to ensure the cooling of cladding; In the typical ADS triggering accident except the 10 inch break accident, the sprayer can all maintain the critical jet for a long time to avoid the chugging or condensation oscillation in the process of direct contact condensation. The sprayer has not reached the critical jet state in 10 inch cold leg break accident, and the influence of low-speed jet should be paid attention to in the design of the sprayer. The arrangement of two independent ADS depressurization pipelines has 100% redundancy. Even if one of the ADS depressurization pipelines does not work properly, the other system can still ensure the safety of the reactor core. The results of this paper can provide theoretical and data bases for ADS pipelines improvement and sprayer design, and also have important significance for the safety operation of nuclear power plants.