An experimental study of n-heptane pyrolysis (2.0% n-heptane in argon) has been performed at low pressure (400 Pa) within the temperature range from 780 to 1780 K. The pyrolysis products were detected by using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). Photoionization mass spectra and photoionization efficiency spectra were measured to identify pyrolysis products, especially radicals and isomers. Mole fraction profiles of pyrolysis products versus temperature were also measured, indicating that H(2), CH(4), C(2)H(2), and C2-C6 alkenes are major pyrolysis products of n-heptane. Meanwhile, the thermal decomposition pathways of n-heptane have been investigated using theoretical calculation. The calculation results are in good agreement with the experimental measurement. On the basis of the experimental observation and theoretical calculation, the pyrolysis channels of unimolecular dissociation are proposed to understand the pyrolysis process of n-heptane.