Abstract: Water soluble high polymer solution has been widely used as fracturing fluid,friction-reducing agent and filtration loss agent in fracturing,drilling and well completion etc.To minimize the damage done to the pay zone by high polymers from adsorption and plugging,a kind of efficient controllable delay breaker has been developed.When synthetic polymers(like crosslinked polycrylamide and its derivatives)is used as fracturing fluid in pay zones with temperature lower than 50℃ and permeability less than I md.,the conventional breaker (inorganic oxidant) is usually inefficient.The Institute has developed a new efficient CB-breaker capable of degrading thoroughly gels in different kinds of water soluble polymer solution (natural or modified vegetable gum,cellulose,synthetic polymer) under temperature higher than 25℃ to minimize damage done to the pay zones.Some modification of prescription and dosage according to the specific conditions of pay zones may do well to control the rate of gel breaking.Laboratory test and field application have both produced satisfactory result.