A new evaluation method, with accompanying software SIUEW1.0, was developed to precisely calculate uniformity from catch-can test data. Water application depths of a rain-bird sprinkler 30PSH were calculated at each grid point. The Christiansen uniformity （CU） for four sprinklers in square and triangular spaced were computed with 1 m and 2 m spaces, and with 1?m and 0.25 m grid spaces. The results showed that the sequence of CUs from high to low is 2 m sampling spaces by linear interpolation, 2 m sampling spaces by cubic spline interpolation, 1 m sampling spaces by linear interpolation and 1m sampling spaces by cubic spline interpolation. CUs computed from 2 m space catch-can data are greater than that from 1m space catch-can data by 3%～4%. CUs computed with cubic spline twice interpolation are less than that with linear interpolation by using nearest four points by 1.0%. The deviation between CUs computed from grid points with 1 m space and 0.25 m separately are less than 1.0%. It could be concluded from these results that the influence of sampling space, interpolation method, and grid space on CU is less and less in turn.