Vehicle load and tire load play an important role in estimating vehicle parameters and vehicle control. In previous studies, the tire load was estimated based on vehicle dynamics. However, the load estimation algorithm based on vehicle dynamics is highly dependent on the vehicle parameters and has a long estimation time and low accuracy. This paper proposes a new load estimation algorithm using an intelligent tire sensor. The proposed algorithm is analyzed through a flexible ring tire model, which is a physical tire model, and is constructed based on the relationship between load-contact angle-pressure. The performance of the load estimation algorithm is verified by indoor tests using Flat trac. As a result, fast estimation times and high estimation accuracy are confirmed under various conditions.