The thermal crosstalk characteristics in high-power 808 nm AlGaAs/GaAs laser diode bar were investigated experimentally and theoretically using infrared thermography and finite element method. We have performed the steady-state and transient analysis. A detailed profile of thermal crosstalk in laser diode bar was presented in this paper. The steady-state temperature rise has a logarithmical dependence on the total operation current, and the thermal crosstalk between emitters increases with the current density. Furthermore, the transient thermal analysis suggested that the thermal crosstalk occurred mainly in chip. Using thermal resistance parallel connection model, we explained the phenomena that the time constant of chip decreased with the increase of total operation current.