Accurate positioning of nanoantennas is critical for their efficient excitation and integration. However, since nanoantennas are subwavelength nanoparticles, normally smaller than the diffraction limit, measuring their positions presents a significant challenge. This is particularly true for locating the nanoantenna along the $z$-direction, for which no suitable method currently exists. Here, we have theoretically developed and experimentally validated a novel light field capable of measuring the 3D positions of nanoantennas accurately. This field’s polarization chirality transitions from right-handed to left-handed along a predefined 3D direction at a subwavelength scale. For a spherical single-element nanoantenna, the polarization components of the scattering field change significantly as the nanoantenna moves, due to the rapid polarization transformation in the excitation light field. By analyzing the polarization components of the scattering field, we can achieve positional accuracy of the nanoantenna along the specified direction close to 20 pm. This work improves the accuracy of transversely distinguishing nanoantennas from 100 pm in conventional methods to 20 pm. Moreover, the positioning of the nanoantenna along three dimensions is all available as polarization transitions can be predefined along arbitrary 3D direction, which is significant for precision measurement and nanoscale optics.