In order to solve the mechanical instability of the initial state of soft polyimide foam, the Solimide^® AC-550 polyimide foam was used for different pressure and pressure pretreatment respectively, and the tensile and compressive properties of the pretreated samples were tested.The results show that the negative pressure pretreatment damages the mechanical properties caused by the foam,and the pre-treatment at +4 kPa can make the foam obtain relatively stable mechanical properties and meet the needs of engineering applications.