The stability of three Ionic liquids (［Bmim］HSO4, ［BPy］HSO4 and ［Bmim］BF4) in DBD (Dielectric Barrier Discharge) Plasma under atmospheric pressure was investigated by using the OES (Optical Emission Spectrometer), UV-Vis (Ultraviolet and Visible Spectrophotometer), FTIR(Fourier Transform Infrared Spectroscopy) and NMR (Nuclear Magnetic Resonance) techniques. The influences of the stability of three Ionic liquids on the crystal phase structure of TiO2 were also studied by preparation of TiO2 with DBD plasma under atmospheric pressure using three kinds of Ionic liquids as assistant, respectively. The results showed that the position and quantity of argon argon plasma emission spectra peak did not change when three kinds of ionic liquid were introduced in DBD plasma. This indicated that the three ionic liquids of above did not evaporate in the plasma area and form excited species. However, the intensity argon emission peak decreased obviously. Both FTIR and UV-Vis spectrospecy of ［Bmim］HSO4 and ［BPy］HSO4 showed no difference before and after plasma discharge. This indicated that the ［Bmim］HSO4 and ［BPy］HSO4 were stable in plasma. There was no significant difference in the infrared spectra of ［Bmim］BF4 before and after plasma treatment. However, the position of the absorption peak in the UV-Vis spectra of ［Bmim］BF4 before and after plasma treatment had a large shift, and the analysis of 1H NMR showed that all the peaks shifted to right 0.2 units approximately. That indicated that the structure of some ［Bmim］BF4 changed in plasma. The XRD spectra of ［BPy］HSO4-TiO2 and ［Bmim］HSO4-TiO2, which were prepared by DBD plasma under atmospheric pressure using ［Bmim］HSO4 and ［BPy］HSO4 as assistant respectively, showed that all the diffraction peaks were the same as the standard spectra of anatase TiO2, and this indicated that ［BPy］HSO4-TiO2 and ［Bmim］HSO4-TiO2 were pure anatase. However, The XRD spectra of［Bmim］BF4-TiO2, which were prepared by DBD plasma under atmospheric pressure using ［Bmim］BF4 as assistant, showed that the diffraction peaks at round 24.1° shifted to lower 2θ values, while the diffraction peaks at around 48.0° shifted toward higher 2θ values. The shift of the diffraction peak for ［Bmim］BF4-TiO2 samples indicated that lattice imperfection was formed due to F doping. The fluorine atoms entered into the lattice of TiO2, therefore breaking the equilibrium of original TiO2 atoms and varying the inter planar crystal spacing of anatase TiO2. This revealed that same of ［Bmim］BF4 were broken down in plasma. The formation of F doped TiO2 photocatalyst also indirectly proved the instability of ionic liquid ［Bmim］BF4 in atmospheric pressure plasma, and this results were the same with the analysis of UV-Vis and 1H NMR. The formation of F-doped TiO2 photocatalytic materials also indirectly proved the instability of ionic liquid ［Bmim］BF4 in atmospheric pressure plasma, which was consistent with the results of NMR and UV-Vis. It was also proved that ionic liquids play an important role in the formation of pure anatase crystals and the promotion of highly reactive photocatalysis materials under the action of plasma. It provides an important experimental and theoretical basis for the preparation of high performance nano-materials by plasma-assisted ionic liquids.