The optical emission spectra are measured during the positive half cycle in a sinusoidal driven needle to plate dielectric barrier discharge in argon andair, and the spatial distributions from needle to plate in the discharge channel of plasma luminous intensity, spectrum width and electric field intensity are investigated. The effect of the dielectric plate on the plasma parameters is also analyzed. According to the intensities of two lines of 763 nm and 772 nm of argon discharge specrtrum, it is found that the intensity from needle to plate increases first and then decreases around the neadle, while it increases rapidly around the plate. The distribution of spectrum width (696.54 nm) is investigated, and the spectrum width increases to maximum around the plate. The distribution of electric field is obtained by calculating the intensity ratio of the nitrogen molecular ion line of 391.4 nm to nitrogen molecular line of 394 nm in air discharge spectrum, the electric field strength decreases first and then increases along the discharge channel. The results show that the dielectric plate playes an important role in the distribution of plasma parameter.