n-Butanol pyrolysis in a flow reactor was investigated at the pressures of 5, 30, 80, 200, and 760 Torr. Synchrotron vacuum ultraviolet photoionization mass spectrometry was used for the identification of pyrolysis species and the measurement of their mole fractions. A detailed kinetic model consisting of 121 species and 658 reactions was developed to simulate the n-butanol pyrolysis. To enhance the accuracy of the model, the rate constants of unimolecular reactions of n-butanol and beta-scission reactions of four n-butanol radicals (C4H8OH) were calculated with the variable reaction coordinate transition-state theory (VRC-TST) and the Rice-Ramsperger-Kassel-Marcus (RRKM) theory coupled with the master equation method. These rates are very sensitive to the mole fractions of pyrolysis species and have been well-validated by the pyrolysis experiment. The model was further validated by the low-pressure premixed flames at different equivalence ratios, oxidation data from the jet-stirred reactor, and ignition delay times. The comparison between predicted and measured results exhibited a good performance of this model. The reaction product analysis and sensitivity analysis were performed to elucidate the chemistry under different conditions.