A method for fabricating a flexible LED light string includes steps: 1: core strip extrusion molding; 2. LED light bead hole punching and cutting mark labelling; 3. inserting the flexible LED PCB into the core strip; 4. extrusion molding for light string sheath, i.e. diffusing strip. With the method, the core strip can has a variety of cross sectional shapes according to design needs. In the same way, the sheath can has a variety of cross sectional shapes according to design needs, and has a variety of combinations of materials and colors through multiple-color extrusion molding, for example, the sheath mixed with colored decorative strips, and non-transparent partially.