Abstract: SONG, a multi-functional lattice code focusing on the core analysis of next-generation reactor systems, adopted Method Of Characteristics（MOC） to solve the neutron transport equation with arbitrary geometry. It can simulate flexibly the two-dimensional fuel subassembly model or core model with rectangular lattice or hexagonal lattice, which consist of pin-type or plate-type fuel elements. To meet the demands of calculation on thorium-uranium and uranium-plutonium fuel cycle with extra-long lifetime and extra-deep burnup, the exponential matrix method is adopted to solve the problem of extended fission products and actinides chain. Verification shows that SONG satisfies the anticipated performance and function requirements.