In view of the problem that conventional annular chemical isolation agent is easy to enter the reservoir with poor annular packing in horizontal wells without interlayers，a high thixotropic annular chemical isolation agent was developed using corn starch，acrylamide，N, N'- methylenebisacrylamide and magnesium aluminum carbonate composite materials as the main raw materials. Annular filling performance，curing performance，and annular sealing performance at different permeability levels was studied，and the pilot testing was carried out. The results showed that the chemical agent had good thixotropy and strong annulus filling ability. Curing time was adjustable from 3 hours to 10 hours. Compared with the comparative test without annulus chemical isolation，the initial water cut decreased from 97.54% to 41.28% after annulus chemical isolation，the time for water cut rising to 98% was delayed from 2 minutes to 35 minutes. when the permeability level was increased from 2.89 to 14.79，the initial water cut decreased and the time of water cut increasing to 98% was extended from 11 min to 35 min，the water control effect was obvious. The technology had been carried out in the field test of 4 wells in offshore oil field，and the water content decreased by 6.14%，the daily oil increase was 30.45 m³ ，the stage oil increase was 0.92×10⁴ m³ ，and the stage reduction of water was 0.98×106 m³ . The chemical isolation technology for the annulus of the screen tube in horizontal wells without interlayer is feasible，and it is recommended to promote its application in segmented water plugging control in screen tube completion horizontal wells.