Because of low fracturing pressure in Rumaila formation, leakage is easy to happen in the intermediate casing cementing procedure; the shale development in production layer leads to irregular chambering and shrunk holes; cementing displacement efficiency is low and it is difficult to guarantee cementing quality. In late well cementing construction, the formation characteristics are analyzed starting from several key factors that affect the cementing quality to optimize the technical measures of plugging and by cementing design software to optimize the number of casing centralizer; through indoor test, inhibited weighted drilling fluid is optimized to control and adjust the performance parameters of drilling fluid used in unstable shale layer, the API fluid loss is controlled at 4mL and density 1.35g/cm3. A set of comprehensive cementing technology is formed, the cementing qualified ratio reaches to more than 80% in field tests.