The DD98M nickel-based superalloy tube is fabricated by using laser additive manufacturing (LAM). The microstructural variations of the as-deposited, solution-aged and long-term aging are studied. The precipitates distribution of deposited and solution-aged alloy were analyzed combining with the study of γ‘ precipitates evolution at 1000 ℃ long-term aging. The results show that the as-deposited microstructure of the alloy mainly consists of epitaxial finer columnar grains with an optimum amount of cubical γ‘ precipitates with around 70 vol. %. No γ-γ‘ eutectic is observed at interdendritic. Rapid solidification during LAM process largely eliminates the segregation of metal elements with an increase of γ‘ precipitates sizes from 210 nm at dendritic arms to 560 nm at interdendritic regions. After solution-aged treatments, γ‘ precipitates (about 370 nm) are uniformly distributed in γ matrix with the sizes distribution fitting the LSW model. During the long-term aging of 500 h at 1000 ℃, no TCP (Topologically Close-Packed) phase exists and the sizes of cubical precipitates have a slight increase. In addition, the micro-hardness of the as-deposited is 442 HV and it will obviously increase to 487 HV after solution-aged heat treatment. Long-term aging reduces around 5.9 % of the maximum micro-hardness.