Tomography is a very beneficial and fundamental technique in the fields of quantum information and quantum optics, which can be applied to infer information about quantum states or quantum processes. In quantum key distribution (QKD), tomography can be proposed to improve the secure key rate by taking full advantage of data from both matched and mismatched measurement outcomes to characterize quantum channels accurately. However, to date, no experimental work has been conducted on it. In this work, we study tomography-based QKD (TB-QKD), and for the first time, to the best of our knowledge, carry out proof-of-principle experimental demonstrations by implementing Sagnac interferometers to simulate different transmission channels. Furthermore, we compare it with reference-frame-independent QKD (RFI-QKD) and demonstrate that TB-QKD can significantly outperform RFI-QKD in certain channels, e.g., amplitude damping channel or probabilistic rotation channel.