Molecular dynamic simulations were applied to investigate the Stokes‐Einstein relation (SER) and the Rosenfeld entropy scaling law (ESL) in liquid Fe0.9Ni0.1 over a sufficiently broad range of temperatures (0.70 < T/Tm < 1.85; Tm is melting temperature) and pressures (from 50 GPa to 300 GPa). Our results suggest that the SER and ESL hold well in the normal liquid region and break down in the supercooled region under high‐pressure conditions, and the deviation becomes larger with decreasing temperature. In other words, the SER can be used to calculate the viscosity of liquid Earth's outer core from the self‐diffusion coefficients of iron/nickel and the ESL can be used to predict the viscosity and diffusion coefficients of liquid Earth's outer core form its structural properties. In addition, the pressure dependence of effective diameters cannot be ignored in the course of using the SER. Moreover, ESL provides a useful, structure‐based probe for the validity of SER, while the ratio of the self‐diffusion coefficients of the components cannot be used as a probe for the validity of SER.