Carbon fiber-reinforced polymer (CFRP) composite has been widely used for structural strengthening due to superior strength-to-weight ratio, good fatigue and corrosion resistance, as well as shape flexibility. CFRP installation was found to be a more attractive way to strengthen tubular structures with complex geometry rather than traditional metallic-based reinforcing methods. Although tubular joints strengthened by using non-prestressed CFRP sheets have been investigated in references, application of prestressed CFRP has not been reported. This paper presents an experimental investigation into reducing the hot spot stress on T-joints made of circular hollow sections (CHS) with prestressed CFRP strengthening. A scheme of prestressed CFRP sheets for the fatigue strengthening of tubular T-joints was proposed. Variables including the prestressing level and CFRP width were considered. Hot spot stress distribution on CHS T-joints before, during and after strengthening was investigated. It was found that the proposed form of prestressed CFRP sheets could effectively reduce the hot spot stress on chord along the weld toe under brace axial tension loading, especially at the saddle point, where the maximum stress concentration factor (SCF) was witnessed in the unstrengthened specimen. The location of the maximum SCF gradually moved from the saddle point to crown point with the increase of prestress.