A new method was provided based on the empirical mode decomposition(EMD) to solve the difficulties of infrared image dim small target detection in complex background of sky and sea. The decomposition in this paper is based on Delaunay triangulation and piecewise cubic polynomial interpolation. Application to infrared images has shown that the performance of the algorithm can detect infrared small target in background of sky and sea exactly and quickly. The method presented in this paper appears instructive from both theoretical and practical points of view.