The analysis of pyrolysis products,especially in-situ detection and analysis of primary pyrolysis products is an important way to understand the mechanism of coal pyrolysis. In this paper,the application of three kinds of on-line pyrolysis coupled with mass spectrometry（MS)techniques,including thermogravimetric-mass spectrometry（TG-MS),flash pyrolysis-gas chromatography-mass spectrometry analysis（Py-GC-MS),and in-situ pyrolysis time-of-flight mass spectrometry（Py-PI/EI-TOF-MS)combined with vacuum ultraviolet photoionization（PI)and electron ionization（EI)in coal pyrolysis were reviewed,and their advantages and disadvantages were compared. TG-MS can be used to analyze the coal conversion and the escape characteristics of pyrolysis gas volatiles（especially the light components)with the pyrolysis temperature. The compositions and distribution of pyrolysis products at rapid heating rate can be acquired by Py-GC-MS. In comparison,due to the characteristic of in-situ analysis,high sensitivity,soft ionization and easy cleaning,Py-PI/EI-TOF-MS can be used to in-situ detect the primary products from individual or co-pyrolysis of coal-model compounds,raw coal and its extraction,biomass as well as waste plastics. The evolution behaviors of primary products and the catalytic pyrolysis can be also implemented. The in-situ Py-PI/EI-TOF-MS provides a promising method to understand the pyrolysis mechanism of carbonaceous organic matters in a molecular level.