Female Rhododendron ‘Nova Zembla’ was used for pollination with male R.excellens.Fluorescence microscope severed as a tool to study the process of pollen sprouting and pollen tube growth after crossing.Capsule setting of the cross was calculated.The results showed as follows:(1)the pollen of R.excellens sprouted and formed the pollen tube in 1 d after pollination.The pollen sprouting rate increased significantly in 1~5 d after pollination and then slowly after that,the highest rate of pollen sprouting was 37.36% in 12 d after cross.(2)The speed of pollen tube growth was from slow to quick after pollen spouted.Pollen tube entered the style in 2 d after the cross,and reached the ovary in 7 d after pollination and then got the ovule in 10 d after the cross.Fertilization of ovules was noticed in the cross,but the percentages of presumed fertilized ovules were very low,with 7.42±0.89 pollen tubes entered the ovules in 12 d after pollination.(3)During the pollen tube growth,it was companied with a series of callose deposited responses,which was happened in the stigma cell,pollen tube,canal cell,ovary and embryo sac in ovule.The pollen tube swollen,spiraled,grew broadly or narrowly,wringed and stopped growth of the tip,pointed tips abnormally or stop growing when callose plug was sedimentary in the tip of pollen tube,the spiraling and wide-diameter and grew reversely during the growth.(4)No capsule set in the cross.The results indicated that the cross between Rhododendron.‘Nova Zembla’ and R.excellens was incompatible.The preliminary inference was that the pollen tube’s abnormal behavior could be the main factor for the inter-species incompatibility,and barriers operated probably both before and after fertilization.