Abstract: For the development of high-end fiber lasers and breaking through the technical bottlenecks limiting the output power and performance improvement of fiber laser systems, the Joint-Innovation Center of High Power Fiber Laser Technology, Institute of Chemical Materials (ICM) of China Academy of Engineering Physics (CAEP) , adopted the mode-tailoring fabrication process technology, theoretically designed and firstly fabricated the 1.5th-generation (1.5G) YDF specialty laser fibers, which are particularly suitable for 976 nm-LD end-pumping method (976-technology route) to effectively improve the threshold of mode instability (TMI) and significantly optimize the beam quality of laser output. Compared with currently widely-used 1.0G Yb-APS fiber, 1.5G YDF specialty laser fiber shows about 20% improvement both in laser output power and beam quality. The 1.5G YDF specialty laser fibers fully demonstrate technical characteristics of “three-high/one-excellent”—high power, high efficiency, high TMI threshold, and M² optimization—which can be selected by high-end customers in the industrial market and/or applied in high power laser fields.