To simulate the microporosity defects of single-crystal blades with Zr contents of 0.001 wt.%, 0.003 wt.%, 0.007 wt.% and 0.012 wt.%, the first-generation nickel-based single crystal superalloy DD416 and its blades were used as the research objects. The simulation results reveal that the microporosity defects are distributed mainly at the blade edge plate and that their content decreases first but then increases with increasing Zr. The experimental results and simulation results show essentially the same trend, and the experiments reveal that when the Zr content is 0.007 wt.%, the porosity defects of the DD416 single-crystal blade are the lowest. An examination of the reasons for this phenomenon reveals that when the Zr content increases from 0.001 wt.% to 0.007 wt.%, the change in primary dendrite spacing is the main factor influencing the formation of microporosity defects. An increase in the Zr content leads to an increase in the diffusion activation energy of solutes during the solidification process of the blades and a decrease in the diffusion coefficient, thereby decreasing the primary dendrite spacing and ultimately lowering the content of microporosity defects. The porosity defect content in the experimental results decreases from 0.463% in 10Zr to 0.064% in 70Zr. However, when the Zr content increases from 0.007 wt.% to 0.012 wt.%, the main influencing factors for microporosity defects are the volume fraction of the γ/γ′ eutectic phase and the solidification range. The content of the eutectic structure further increases, the solidus temperature of the alloy decreases, and the solidification range expands, resulting in an increase in microporosity. The porosity content in the experimental results increased to 0.493%.