This study aimed to evaluate the safety resilience in process industries with a passive defense approach in South Pars Phase 19 refinery. This descriptive-analytical study was conducted in the period 2018 to 2020. The study sample included sweetening unit of South Pars Phase 19 gas refinery. Based on the three main components of probability, severity, and preparedness, a semi-quantitative model used for evaluating safety resilience in process industries. Data analysis performed using SPSS v.25 and AMOS v.24 software. 131 sources of danger were identified. 21.4% of the identified hazard elements are in the weak threat range, 59.5% are in the moderate threat range, and 19.1% are in the severe threat range. The maximum and minimum values ​​of the present study's resilience index were 500 and 10, respectively, and are related to the risk element of utility cut-off and instrument cut-off. The results showed that the resilience index is generally predictable up to 91%. The three components of probability, severity, and preparedness predicted the resilience indicators with values ​​of 0.39, 0.78, and 0.37, respectively. The findings indicated that severity index is the most crucial component in determining the vulnerability and resilience parameters of the system due to the nature of the process and critical parameters in refineries. Therefore, resilience assessment, attention to the severity of possible consequences, and the establishment of different protective layers to reduce the amplitude and severity of damage caused by catastrophic events is the most vital principle to increase process systems' resilience levels.