Abstract: The relationship between the viscosity of Luojia ultra-heavy oil from Shengli oil field and its polar fractions, heteroatoms, metallic elements was investigated. It is found that the high viscosity of the oil is related with three factors: resin and asphaltene with high molecular weight, high sulphur content and the enhanced cohesion of asphaltene by macrocyclic compound formed by V, Fe and Ni. Simultaneously the effect of the viscosity reduction was examined. The interfacial tensions of water-oils are reduced greatly by the viscosity reducing agent, thus the viscosity of the ultra-heavy oil is reduced. The electron microprobe pictures of asphaltene is compared before and after treatment .On the basis of these evidences it can be concluded that the viscosity reducing agent can infiltrate into plate-like asphaltene molecules by forming hydrogen bond, infiltration and dispersion, so that the order of aggregation of the plate-like asphaltene molecules is lowered and the plate-on-plate aggregations become randomly packed ones.