Abstract: A simulated gastrointestinal tract (GIT) model was used to research the effects of different particle size and different chain length lipids on the physicochemical properties, microstructure and bioaccessibility of β-carotene in oranges during digestion process of excipient emulsions. The results showed that, compared with medium particle size (500 nm) and large particle size (10 μm) emulsions, the physical properties (particle size and potential) and microscopic morphology of small particle size (200 nm) emulsions showed the most significant change in each simulated digestion stage. Except for the small intestine phase, the physical properties of the excipient emulsion prepared from the medium-chain oil (represented by MCT oil) had no significant difference from that of the long-chain oil (represented by corn oil) (p>0.05). The emulsions of small particle had the fastest digestibility of oil and its bioavailability (38.13%) was significantly higher than that of medium size emulsions (24.93%) and large particle emulsions (26.23%) (p<0.05). There was no significant difference in lipid digestion rate between long chain lipids (represented by corn oil) and medium chain lipids (represented by MCT oil) (p>0.05). Compared with medium chain lipids, the excipient emulsion prepared from long chain oils had a more significant effect on improving the bioaccessibility of β-carotene (p<0.05). This experiment had great significance in guiding the design of excipient emulsions to increase the bioaccessibility of lipophilic bioactive substances in fruits and vegetables.