A 3D laser machining system comprises: a move state simulation unit that simulates a move state of a machining head using 3D CAD data about a workpiece containing material information defining thermophysical properties and 3D CAD data about a machining head under a condition of moving the machining head relative to the workpiece while the machining head is maintained at a predetermined angle a predetermined distance along a machining line in virtual space; a thermal fluid simulation unit that conducts non-stationary thermal fluid simulation for obtaining a temperature distribution in a region covering the workpiece to be changed by the move of the machining head outputting a laser beam; and a machining condition setting unit that sets a laser machining condition containing a relative move condition for the machining head and a laser beam output condition before laser machining on the basis of results of the simulations.