The ultrafine Powder plugging agent is a highly effective new plugging agent， composed of 20%—30% superfine oil well cement，10% —15% nano-CaCO3，3% —5% ultrafine CaO，15% —20% nano-oxide containing silicon，iron and aluminum elements，3%—5% Na-bentonite，2%—3% NaCO3，1%—2% Phosphate，1%—2% Fe-Cr-lignosuifonate（FCLS），0.5%—1% HECMC，1%—2% AMPS and 1%—3%NaOH. According to different water-cement ratio，a series of ultra-fine plugging agents with different density was prepared，and its performance，such as the rheological property，the solidification time，the plugging rate to the cores，the compressive strength of the solidified body，and so on，was comprehensively evaluated by laboratory experiment，and the field application was carried out. The research results showed that the viscosity of the plugging agent with density of 1.4—1.8 g/cm³ was less than 35 mPa·s，the injectivity of the plugging agent was good，which could be injected into deep formation pore easily. Suspension of the plugging agents was good，when the density was greater than 1.6 g/cm³，Plugging agent slurry was hardly separated. The curing time of the plugging agent slurry could be adjusted，and the construction was safe，its initial setting time was 2.7—18.5 h，final setting time was 3.1—28.1 h. after the plugging agent slurry was cured，the solidified body（SB）did not contracted，the compressive strength of the SB was over 25 MPa，the SB was resistant to high temperature of 130℃ and salt of 20×104 mg/L. The plugging rate of plugging agent to the cores with different permeability of 20.5×10^-3—127×10^-3μm² was up to 99.9%，moreover，the outwash resistance and high temperature tolerance was good. The plugging agent had certain solubility，and the permeability recovery rate of the plugged cores was over 50% after the acid rock reaction. The field squeezing and plugging technology was applied in Wei 360 block of the low permeability reservoirs for 27 well times，the technological success rate reached 100%，and the effective rate of increase in oil production reached 100%.