Wetting of structure material with liquid metal is one of the key influence factors on liquid metal embrittlement （LME） effect. In order to investigate LME mechanism for T91 in liquid Pb alloys, contact angles and interface interaction of molten Pb/ PbBi alloy on T91 were studied with sessile drop （SD） method and microscopic examination. The results indicate that the contact angle of T91 with molten PbBi is larger than that with Pb at the same temperature, and all the contact angles are larger than 90°. Moreover, the contact angles decrease with the increase of the temperature when the temperature is under 400 ℃, but they remain constant when the temperature is higher than 400℃. SEM examination shows that there is no obvious reactivity on the interface of both systems. The decrease of interface tension between liquid PbBi alloy and gas is caused by the surface segregation of Bi atoms, which might lead to the contact angle of T91 with PbBi is larger than that with molten Pb.