A molecular structure of propyl-nitrate is calculated by using ab initio calculation method. The calculation results indicate that NO₂ radical is fallen away more easily. The delay time of shock ignition is determined by using the method, i.e. intermediate product of the most early emergence for the loaded propyl-nitrate is determined at first with spectrometer, the emergence of intermediate product of NO₂ for propyl-nitrate after shock ignition is always the most early. The monochrometer is adjusted to 463 nm wave length of NO₂, and the time of arriving for shock wave is measured with gauge. The delay time of shock ignition for propyl-nitrate is determined. The delay time determined by the method is closer than that of by using photo-electric diode whose peak wave length is about 800 nm. The measurement results show that the emergence of intermediate product of O for propyl-nitrate after shock ignition is different,and radiation intensity for the radicals is also different. The emergence times for O,NO₂,CO,C₂,CH,CO₂,H₂O radicals is obtained after the shock wave enters into the propyl-nitrate. The emergence time of NO₂ radical is the most early. The method combined the theory with the experiment may obviously decrease tests to determine shock ignition time.