Abstract: Three-phase separator is an important device used in the development of offshore oil and gas fields to separate the oil, gas and water, for which proper pressure setting value is very critical. Herein, three-phase separators of A and B offshore platforms were taken as the object of research, and a dynamic simulation model of process was established based on the field operation conditions with K-Spice software. Specifically, the internal pressure change of the separators was simulated under two conditions, i.e. the gas outlet pipeline blocked and the control valve on the gas outlet pipeline of the separators stuck, and comparison was also made with the pressure setting value recommended by the domestic and foreign industry specifications. The results indicate that: For the setting value of high-high pressure for shutdown is low, the sticking of control valve at the gas outlet of separator may result in the shutdown of oil fields, and under the condition that the gas outlet is blocked, the problem concerning the non-independence of primary protection measure(close the shutoff valve)and the secondary protection measure(open the safety valve for pressure relief) may occur. Therefore, a new method of pressure setting was proposed, that is, to determine the minimum setting value of high-high pressure for shutdown according to the fluctuation value of internal pressure of the separator with the control valve on the gas outlet pipeline stuck, and to determine the minimum value of the setting pressure of the safety valve according to the pressure change of separator with the gas outlet blocked. The new method for pressure setting of three-phase separators can avoid the problem of "production shutdown" caused by the sticking of control valve of the separator and ensure the independence of the primary and secondary protection measures of separators.