Plasmonic photothermal conversion on metal nanostructures has attracted much attention because of its quick response and its local effects. In this work, we built an in-situ two-dimensional temperature measuring system with high resolution and wide temperature range to quantitatively evaluate the photothermal conversion. We analyzed carbon, Au, and Ti nanostructures. The results suggested that the photothermal conversion efficiency per unit volume was higher for plasmon resonance than that of conventional dye absorption.