In order to explore the cause of serious emulsification of the Jimsar crude oil，the crude oil was separated into three components，including colloid，asphaltene，and remaining components，using precipitation and chromatographic separation methods.The elemental analysis of the crude oil and colloid was determined by elemental analyzer. The molecular composition of the heavy oil and the colloid was identified by electrospray technology（ESI）combined with high-resolution Fourier transform ion cyclotron resonance mass spectrometer（FT-ICR MS）. The results showed that the colloid content of the crude oil was 43.19%，the asphaltene content was 0.31% and the residual content was 56.5%. The elemental analysis results showed that the nitrogen content in the colloid was about 2.3 times as high as that of the crude oil，the content of O and S in colloid was 1.82 and 1.29 times as high as that of crude oil，indicating that the main emulsifying active components of Jimsar crude oil came from colloid. In the -ESI mode，the relative molecular weight of non-alkaline compounds was within 200—600 Da and the mass center of crude oil and colloid is at m/z= 350. The molecular structure type and relative abundance of various compounds in the mass spectrum were then analyzed. The content relation of each component in the mass spectrum was，N₁>N₁O₁>N₁O₂>O₂>O₁. It is speculated that the higher content of carbazole（N₁）compounds leaded to the increase of the emulsification and water-binding capacity of the crude oil；in addition，N₁O₁ and N₁O₂，the oxidation products of N₁，increased the hydrophilicity，polarity and emulsification of the crude oil. The structure of O₂ （acid）and O₁（phenol）was also analyzed. Their existence further enhanced the emulsification ability of the crude oil. In the +ESI mode. The molecular weight of the alkaline compounds of Jimusar crude oil and its colloid was within 200—600 Da. The mass center of crude oil was at m/z=350，while the mass center of colloid was at m/z=340. In the +ESI mode，there were two types of nitrogen-containing heteroatoms，N₁ and N₂，of which N₁ domained the absolute predominance，which may be compound of octahydroacridines，octahydrophenanthridines，quinolines or isoquinolines. Such substances enhanced the emulsifying ability of crude oil under acidic，neutral or high temperature conditions. It was inferred that the main cause of the serious emulsification of Jimusar shale oil was the polar components in the colloid，which had high interfacial activity and were easily adsorbed on the interface to promote the reduction of interfacial tension and the increase of interfacial membrane strength，hence was conducive to the stable existence of the emulsion.