Abstract: In view of the problem that downhole pressure fluctuations cause the qualified rate of stratified water injection to drop rapidly in low permeability reservoirs, a downhole small-volume water nozzle was designed with a self-adjusting mechanism. It was then integrated into the downhole constant-flow stratified water distributor using a concentric bridge, which would minimize pressure fluctuation-triggered stratified flow variations. On the basis of the Bernoulli principle, with theoretical analysis and laboratory experiment, a self-adjusting mechanism was designed to achieve the stratified and constant flow water injection with small flow rate. According to laboratory experiments, the self-adjusting mechanism can be adjusted within an injection pressure range of 0.2−1.5 MPa. Adopting the water nozzle mechanism, the downhole constant-flow stratified water injection technology with concentric bridge has been applied in more than 40 wells in the low permeability reservoirs of Changqing Oilfield. It is possible to achieve an increase of injection pressure rise by 1.5 MPa without manual intervention, and the stratified flow adjusted automatically until the injection is qualified. The field application in Changqing Oilfield showed that the technology could increase the qualified rate of stratified water injection from 43.4% to 75.0% within 6 months and reduce the testing and adjusting frequency from 4 times to 2 times per year. It can also prolong the testing and adjusting period of the involved wells so that the annual operation expenses for a single well can be reduced by 26 000 yuan.The stratified water injection technology proposed has provided an efficient stratified water injection method for fine water injection development in low permeability reservoirs.