An experimental study is made on the selection of parametersof the correlation function, the relationship between the observational station distribution and the interpolation coefficients, the method of determining interpolation coefficients, and the influence of the first guess field on the interpolation in the objective analysis method of theoptimum interpolation. A scheme is thus established for the mono-element and multi-element interpolation in the 12-layer variable area and gridof four elements. The analysis of the elements and that of the elementlayers in the scheme are both variable. In the multi-element scheme,the multivariate optimum interpolation is used for the height and wind component (u, v), whereas the mono-element interpolation is used forthe relative humidity.