The evolution of high-mass star formation has remained a mystery over the years due to limitations from observational challenges. We present the first successful Karl G. Jansky Very Large Array (JVLA) dust-polarization observations at ~7 mm wavelengths towards a high-mass star-forming region, G31.41+0.31. Our target source represents the best studied case in the previous Submillimeter Array (SMA) and Atacama Large Millimeter Array (ALMA) observations at <1.3 mm wavelengths. Intriguingly, the B-field morphology resolved at 7 mm and 1.3 mm wavelengths appears dramatically different. Possible explanations to the angle offset include different polarization mechanisms, and large-scale and small-scale fields probed by different wavelengths. We make use of radiative transfer modeling to construct a magnetic field model that can consistently explain the two sets of polarization angles. This can provide information on the polarization mechanisms and the magnetic field structures in regions of different densities and scales of the clump. Our observation results indicate that dust polarization observations at long wavelengths are essential to understand the structure of magnetic fields and their roles in high-mass star-forming regions. We foresee that the ALMA Band 1 receivers (30-50 GHz) will lead to a breakthrough in this area in near future.