Abstract: Hydrothermal vent fields are crucial components of the mid-ocean ridge hydrothermal circulation system, and their heat flux and flow field characteristics directly affect the material transport and energy exchange processes within hydrothermal systems. Due to the complexity of the deep-sea environment and limitations in observational techniques, current understanding of plume flow field characteristics remains limited, and the methods used for heat flux estimation are of relatively low accuracy. This study centers on the DFF6 high-temperature hydrothermal vent in the Longqi hydrothermal field along the ultraslow spreading Southwest Indian Ridge. By integrating particle image velocimetry (PIV) technology with the Morton-Taylor-Turner (MTT) semi-analytical steady-state turbulent jet model, we conduct a quantitative investigation on the flow field structure and heat flux of the vent. Results indicate that the DFF6 hydrothermal plume exhibits a typical turbulent structures under the context of an ultraslow-spreading ridge, with significant lateral deflection caused by ambient bottom currents, causing lateral displacement of the plume. Within a certain range, the vertical velocity of the plume increases with rising elevation, reaching a maximum vertical velocity of 48.6 cm/s. The estimated heat flux of the DFF6 vent is approximately 66.15 MW, with a maximum plume rise height of 167 m and a buoyancy frequency of 1.8×10⁻³ s⁻¹. This study refines the estimation method for heat flux in deep-sea hydrothermal systems, enhancing the application of PIV and MTT models in hydrothermal plume dynamics research and providing critical support for the study of material and energy cycles in submarine hydrothermal systems.