There were some problems in mid-deep water-flooding reservoir of Jidong oilfield，such as injection water forward one-way，big difference of water injection profile，and the difficulty of injection production adjustment. So silicate gel plugging agent was developed using silicate，water retention agent and activator. The gelling principle of silicate gel plugging agent was analyzed，the injectivity and plugging performance were studied，and the field application was carried out in Jidong oilfield. The results showed that when the mass ratio of silicate，water retention agent and activator was 5∶1∶0.2，the plugging rate of plugging agent to media and low permeability sand pipes was 93.5% and 97.3% respectively，showing good injectivity and plugging ability.The plugging agent had good injection selectivity which preferred to plug higher permeability layer. The diversion rate of low permeability sand pipe increased from 29.8% to 85.2% and that of high permeability sand pipe decreased from 70.2% to 14.8%. The gel strength was improved by the cross-linked network structure coated with silicate gel and silicate precipitate. After the silicate gel plugging agent was applied in 6 wells on site，the average water injection pressure increased 4.67 MPa，the water injection profile was improved and water injection volume was increased. There were 8 corresponding wells which had an obvious effect of increasing oil production and decreasing water cut and the cumulative oil increment was 4314 t.