The invention discloses an off-line flame chamfering device for a continuous cast slab. The off-line flame chamfering device comprises a workbench, a chamfering table rack car, a traction assembly, a supporting frame and a flame chamfering assembly, wherein the chamfering table rack car is slidably arranged on the workbench; the traction assembly is arranged on the workbench and is connected with the chamfering table rack car; the supporting frame is spanned at two sides of the travelling route of the chamfering table rack car; the flame chamfering assembly is arranged on the supporting frame and can move along the supporting frame; and the moving direction of the flame chamfering assembly is vertical to the travelling direction of the chamfering table rack car. The chamfering device is high in accuracy and adaptability, energy-saving and environment-friendly in use and capable of increasing chamfering efficiency and improving chamfering quality.