The work aims to study the effect of the change of surface roughness of the substrate to be deposited on the quality of the deposited layer (macroscopic morphology, microstructure and mechanical properties) by laser, so as to obtain a deposition layer with excellent morphology, texture and properties. Single-channel single-layer, thin-wall, multi-pass and block deposition experiments were carried out on the surface of P20 steel substrate under different surface roughness with 316L stainless steel powder to obtain the deposition layer required for test analysis. OM, SEM and tensile test were used to analyze the microstructure of the deposition layer. Single-channel single-layer: compared with the deposition layer on the surface of the milled substrate, the deposition layer on the surface of the sandblasted substrate had a melting height and melting depth of 100%, while the melting width increased more slowly. Single-channel thin wall: in the deposition of the first five layers, the surface deposition height of the sandblasted substrate increased to 2.5 mm. The surface deposition height of the milling surface was only half of the former, and the internal porosity of the deposition layer on the sandblasted substrate was only 31% of the milling substrate. Multi-pass: the internal growth range of the longitudinal dimension H of the deposited section continued to become larger as the roughness increased, while the lateral dimension L range remained stable. Mechanical properties: σb on the surface of the sandblasted substrate was 540.93 MPa, and σb on the milled substrate was 523.12 MPa. With the increase of the surface roughness of the substrate, the trapping effect of the deposition process is correspondingly enhanced, and the macroscopic topography of the single-channel single-layer deposition layer is increased; For thin-walled deposition, the effect of substrate roughness on thin-wall height is mainly concentrated in the first 5 layers. The increase of roughness makes the deposition height increase and the internal porosity decrease. When multi-pass is used, the greater the roughness, the larger the dimensional change in the direction of the melt penetration. The dendrites inside the deposition layer are coarser and uneven. The tensile strength inside the deposition layer increases as the roughness increases.