Abstract: Fractures or cracks sealing materials deployed in conventional evaluation methods displayed unsatisfactory plugging performances in tight oil formations of the Daqing Oilfield.Under such circumstances,an innovative stainless steel powder sheet was pressed by special technique to simulate cracks in micro/nano meter scales. In addition,devices to evaluate plugging performance with high precision and reasonable repeatability was designed and made. Lab test results showed that the innovative plugging performance evaluation technique could be used to replace the fluid flow tests under HTHP.Test results showed that the selected drilling fluid displayed satisfactory plugging performances against fractures in micro/nano meter scales.The formula and its add-ons of plugging material were optimized to produce water-based drilling fluids with high plugging performance.The drilling fluid has been used in Well F38-P1 in the Daqing Oilfield to solve the problems of wellbore breakout and wellbore in stability.The innovative techniqueis characterized by simple operations and high accuracy,and can be used to assess plugging performances of drilling fluids under simulated bottomhole temperatures.The new technique may provide necessary technical support for high-efficiency development of tight oil reservoirs in the Daqing Oilfield.