The water-flooding development in ordinary heavy oil reservoirs faces the problem of low oil recovery due to high crude oil viscosity and serious fingering. It is urgent to change the development method to further enhance oil recovery. Taking the ordinary heavy oil reservoirs in Block B21，Gudao Oilfield as the target area，through numerical simulation，we established the boundary chart of the reasonable viscosity ratios between the displacing phase and crude oil for polymer flooding in reservoirs with different crude oil viscosity. Through indoor viscosity-increasing experiments，we determined the polymer concentration limit applicable to the target area. Then numerical simulation was conducted to optimize and determine the best polymer injection concentration. Combining physical simulation experiments，we optimized the alternate in? jection method of high and low concentrations，thereby greatly improving oil recovery under the same polymer usage. Considering development effect and economic efficiency，the usage chart of economic limits under different crude oil and polymer prices was formulated，which can significantly guide the economic and efficient development of polymer flooding in ordinary heavy oil reservoirs. Field application results showed that as of July 2021，the daily oil production has witnessed a maximal increase of 156 t/d from 285 t/d to 441 t/d，and the composite water cut has seen the largest decrease of 12.9% from 89.1% to 76.2%. The cumulative oil increment was 61.4×104 t，and the oil recovery has improved by 7.0%，achieving an obvious effect of oil production increase and water cut decrease.