Accelerated ageing tests have been carried out for polysilazane adhesive in high-temperature and high-humidity environments. After 90 days' accelerated ageing tests the lap shear strengths of adhesive specimen increased by more than 50%. In high-temperature and high-humidity environments adhesive postcure strengthening and humid interface weakening occured simultaneously, but the former is much larger than the latter. The accelerated ageing results after 90 days combine the ageing mechanism showed that polysilazane adhesive had good high-temperature and humidity resistant properties, which indicated the relatively long storage lifetime of this adhesive.