In order to solve the blockage problem during the oilfield development，the representative X-5 crude oil in one Xinjiang oilfield was studied. The components of the crude oil and the blockage in both wellhead and wellbore were also studied to analyze the origin of blockage. The average structure of asphaltenes derived from crude oil，wellhead blockage and wellbore blockage were all measured，and the evolution of wax deposits for X-5 crude oil was further analyzed. It was shown that the stability of X-5 crude oil was poor and the asphaltene was easy to get aggregated and deposited. The aromatic carbon ratio（fA）of the asphaltenes derived from crude oil，wellhead blockage or wellbore blockage increased successively，which was 0.46，0.52 and 0.65，respectively. It was supposed that the asphaltenes with higher fA in crude oil were easier to aggregate and deposit. Consequently，the wellbore blockages mainly consisted of asphaltenes with higher fA. The asphaltene with lower fA was hard to form precipitates，however，it could form blockages with the participation of sand. The sand and the deposited asphaltene in oil wells were the key factors leading to blockage in the wellhead and wellbore. In addition，the wax deposits also led to the blockage of oil well.