The spatial data are processed via editing, query and other complicated analysis with spatial arithmetic operators provided by Oracle Spatial and SQL. In general, abnormal conditions will not occur in the operation with spatial arithmetic operators. In case the number of points of a polygon reaches 60000 or the number of inner rings of a polygon exceeds 200, errors may occur in the intersection overlay operation for spatial geometrical data and the connection between the system and Oracle database will be interrupted. For specific situation of GIS application in China, a polygon of a single parcel, as may occur in land resource investigation, sometimes includes 90000 points, even exceeding 120000 points, and the number of inner rings may far exceed 200. A bug is discovered by the authors in the application of spatial overlay analysis on the national city and county administrative map and national land use map at scale of 1:4000000. After a lot of tests and discuss with Oracle Corporation, the bug is finally confirmed by Oracle Corporation as a new bug (with bug ID of 3146244). To address the limitation of Oracle Spatial in processing vast massive spatial data, an algorithm of "Coordinate reduction intersection overlay" is presented after deeply analyzing the cause of the bug. The appropriate thresholds are decided depending upon the accuracy of analysis for spatial data overlay. Furthermore we have developed an extended module based on this algorithm. The correctness and validity of the solution on the algorithm have been testified by using the same spatial data in which the bug occurred for Oracle Spatial. The study results have been used in the land resource investigation and other fields in Zhejiang province of China.