Abstract: In open hole completion or long interval acidizing with complicated downhole conditions such as casing deformation and formation non-homogeneity, no specific tools can be used for zonal separation. Water base foam slug was used to solve this problem in foreign countries by using the diverting effect of the foam slug, and good result was achieved. The zonal separation mechanism, technical keys, field using and application results were presented in this paper, and it showed that besides the remarkable zonal separation effect, this technology also has such advantages as easy operation and control, low cost, good application potential, and it is an effective way for long interval acidizing.