In the present paper, we make a detailed analysis for the QCD corrections to the electroweak ρ parameter by applying the principle of maximum conformality (PMC). As a comparison, we show that under the conventional scale setting, we have Δρ|N3LO=(8.257-0.012+0.045)×10-3 by varying the scale μr∈[Mt/2,2Mt]. By defining a ratio, ΔR=Δρ/3Xt-1, which shows the relative importance of the QCD corrections, it is found that its scale error is ∼±9% at the two-loop level, which changes to ∼±4% at the three-loop level, and ∼±2.5% at the four-loop level, respectively. These facts well explain why the conventional scale uncertainty constitutes an important error for estimating the ρ parameter. On the other hand, by applying the principle of maximum conformality scale setting, the four-loop estimation Δρ|N3LO shall be almost fixed to 8.228×10-3, which indicates that the conventional scale error has been eliminated. We observe that the pQCD convergence for the ρ parameter has also been greatly improved due to the elimination of the divergent renormalon terms. As applications of the present QCD improved ρ parameter, we show the shifts of the W-boson mass and the effective leptonic weak-mixing angle due to Δρ can be reduced to δMW|N3LO=0.7  MeV and δsin2θeff|N3LO=-0.4×10-5.