To further improve the quality of microalgae-derived bio-oil, the characteristics, kinetic parameters and product distribution of the co-pyrolysis of polypropylene (PP) and Chlorella vulgaris (C.V) were studied by thermogravimetric analysis (TGA) and pyrolysis gas chromatography/mass spectrometry (Py-GC/MS). The TGA results showed that with the increase of the PP amount, the peak temperature of maximum pyrolysis weight loss of C.V decreased, but the trend of PP was opposite. Compared with the experimental and theoretical values, it was found that the residual amount of solid coke and the total activation energy required for co-pyrolysis were significantly reduced, which indicated that there was an obvious synergistic effect during the co-pyrolysis process. The Py-GC/MS results showed that when the PP mass ratio was 0.75 and the final pyrolysis temperature was 500 ℃, the reaction activation energy and hydrocarbon yield had the best synergistic effect. Moreover, the co-pyrolysis of C.V and PP promoted the formation of aliphatic hydrocarbons, inhibited the aromatisation and Maillard reactions, and hindered the formation of aromatics, nitrogenous compounds, acids and oxides.