A new type of large area linearly coaxially coupled microwave plasma source has been developed. In order to obtain the plasma density and its special distribution of this new type of plasma source, Langmuir probe method is used to diagnose the discharge characteristics of the source under different discharge parameters. Three elements, in?cluding influence of microwave power, total gas flow ( the discharge gas is the mixture of hydrogen and argon gases, while the flow ratio of hydrogen and argon gases is 3∶ 1) and the distance Z from the quartz tube were used to design orthogonal experiment. Therefore, the influence of macroscopic discharge parameters on plasma parameters is studied. The test result showed that the electron density of the plasma is above 1010 cm-3 . The horizontal distributions of plasma parameters at the position 14 cm away from the quartz tube were diagnosed to get the best region of films deposition. At last the silicon thin films were deposited according to the plasma diagnosis. An X?ray diffraction ( XRD) spectrum shows silicon films of deposition are polycrystalline silicon thin films and the Raman spectra results revealed that the crystalline ratio of the films is above 92% and the deposition rate of the films is about 8 nm/min.