In order to prevent the spacecraft from being damaged due to the high pyroshock of the separation nut， an orifice is used to suppress the pyroshock response of the separation nut during separation. Throttle holes with three diameters of Φ2 mm， Φ4 mm and Φ6 mm are set on the powder gas channel of the separation nut. The pressure， acceleration and preload of the separation nuts of different orifices in the separation process are tested simultaneously， so as to analyze the separation process of the separation nuts. According to the sequence of movement， the pyroshock load is decoupled into three types of pyroshock sources： powder combustion， preload release and piston impact. The time-acceleration （a-t） curve is transformed into a shock response spectrum （SRS）， and the contribution of each shock source is calculated. The relationship between the orifice diameter and the shock response is obtained. The results show that in the frequency domain of 500 to 10000 Hz， the contribution of gunpowder action is 8.3% to 11.0%； the contribution of preload release is 44.0% to 51.5%； and the contribution of piston impact is 40.2% to 45.0%. The maximum pyroshock response during the separation process is： 1416 g （Φ6 mm）， 1251 g （Φ4 mm） and 852 g （Φ2 mm）. It can be seen that the use of the orifice can effectively suppress the impact response of the separation nut.