After years of waterflooding and polymer injection development in Daqing Oilfield, the recovery potential of the remaining oil in the first type reservoir is decreasing year by year, and the main reservoir of polymer injection is gradually transforming into the second type reservoir. However, due to the characteristics of low permeability and serious horizontal and vertical heterogeneity in the second class reservoir of Daqing Oilfield, compared with the first class reservoir, the field application of polymer flooding is more difficult, and the oil recovery effect of polymer flooding needs to be further improved. In this paper, the reservoir and fluid characteristics of the second class reservoir in Block B of Daqing Oilfield are taken as the research object, and the best injection parameters and injection methods suitable for the target reservoir are optimized by carrying out the laboratory displacement experimental study of the heterogeneous core model. The experimental results show that: with the increase of polymer molecular weight and solution concentration, the size of polymer molecular aggregates increases, the resistance coefficient and residual resistance coefficient increase, but due to the influence of core pore throat shear, the increase of residual resistance coefficient gradually decreases. It can be seen from the oil displacement experiment that the influence of polymer injection viscosity on the production effect is as follows: gradient viscosity increasing > alternating viscosity changing > Gradient viscosity decreasing > single high viscosity > single low viscosity. Among them, the oil recovery of gradient viscosity increasing, alternate viscosity changing and gradient viscosity reducing increased by more than 20%, and the oil recovery of gradient viscosity increasing was the best, with an increase of 24.2%. The influence of polymer injection rate on mining effect is as follows: gradient increase > single high speed > alternate speed change > Gradient decrease > single low speed. Among them, the gradient growth rate and alternating variable rate oil recovery increase greatly, and the gradient growth rate oil recovery increase is 25.6%. Under the condition that the injection slug size is fixed, the increasing effect of recovery under different combination injection methods is as follows: increasing speed and reducing viscosity > decreasing speed and increasing viscosity, and the increasing range of recovery under the combination of increasing speed and reducing viscosity is 28.6%. It can be seen that the combination of changing injection speed and viscosity at the same time in the process of injection is better than that of single changing speed or viscosity.