The exploration and development of petroleum is spread all over the country, and the application of its products is inseparable from the industrial and agricultural production and the daily life of the people. In the use of petroleum and petroleum products, they leak into the soil and accumulate, which will destroy the ecological environment. Laser-Induced fluorescence （LIF） is an important method to detect petroleum hydrocarbon organic pollutants in soil. Laser pulse energy is an important experimental condition of LIF. It has a significant impact on detection sensitivity and stability. In order to explore the characteristics of LIF signal of petroleum hydrocarbons in soil with the pulse energy of excitation light, taking oil as an example, soil samples with machineoil concentration of 0.5%～6% were prepared in the laboratory. The Nd∶YAG laser was used as an excitation source with a wavelength of 266 nm. The fluorescence spectrum of the oily soil at different energy densities was obtained by changing the pulse energy of the 266 nm laser. The experimental results showed that the fluorescence intensity of the oil in the soil had a good linear relationship with its concentration at different energy densities. The fluorescence intensity of the machineoil in the soil itself and in the soil increased as the laser pulse energy increased. The experiment found that as the laser energy density decreased, the average relative error of the LIF system when measuring the oil first decreased first and then increased. The reason was that when the laser energy density was less than a certain range, the signal-to-noise ratio of the signal decreased. Therefore, the average relative error of the measurement gradually increased; when the laser energy density was larger than a certain range, although the signal-to-noise ratio of the signal increased, it had gradually exceeded the optimal measurement range of the system, so the average relative error of the measurement gradually increased. When the laser energy density wasin 2.4~4.0 mJ·cm-2, the fluorescence intensity of the oil in the soil increased linearly with the laser pulse energy density, and the measurement error of the machine oil concentration was less than 2.5%. At this time, the system limited the detection of machineoil to between 200~300 mg·kg-1. When the energy density was greater than 4.0 mJ·cm-2, the increase of the fluorescence intensity of the machineoil was significantly reduced, and the measurement error also increased. Therefore, taking into account the system to measure the average relative error of the machineoil in the soil and the measurement limit, the laser pulse energy was preferably 2.4~4.0 mJ·cm-2. In this paper, the characteristics of the fluorescence signal of the machine oil in the soil as a function of the excitation light energy were studied. The method could be extended to study the fluorescence signals of other petroleum hydrocarbons in soil. This paper provided a reference for the formation of LIF system to measure petroleum hydrocarbons in the site and select better laser energy conditions.