Almost no in situ seismic data are available for Venus; therefore, we can constrain the deep structure of this planet only from the geodetic data obtained by spacecraft. Of particular interest is Venus's core-mantle boundary, which holds clues about the origin and evolution of this celestial body. In this study, we build a series of different mantle/core models of Venus based on several mantle composition models and compare their associated Love numbers k2 with the observed values. Due to the large uncertainty in the observed values of k2, the state of Venus's core cannot be reliably constrained. However, the expected precision of k2 obtained by the EnVision mission will sufficiently reduce the acceptable model space and contribute to estimating the mantle viscosity structure. Based on current geodetic data, we find that the bottom of Venus's mantle may not feature a phase transition from perovskite to post-perovskite if the FeO content of the mantle is less than 8.1 wt%; this region may be different from Earth's D” layer. Furthermore, we find that the combination of observed k2 and Q can be used to distinguish whether the lowermost part of Venus's mantle is a high-temperature basalt layer or a thin thermal boundary layer if observations of Q can be obtained.