A continuous construction method of a side mold-coupled line-type lighting system, the system comprising: two fixed frames for the line-type lighting system each having a basic C-shaped cross sectional structure formed with a closing portion, opposite side walls, and an opening portion, wherein a protruding locking portion for guiding fixation of pieces is formed on each inner side of the opposite side walls, and a side mold coupling end is formed at each of the end portions of the opposite side walls; a diffusion plate coupled with the opening portion of the fixed frames; and a side mold formed in an L-shaped or T-shaped cross section, wherein an engaging portion to be coupled with the side mold coupling end is formed on one of the two types of side molds and coupled with each of the end portions of the opposite side walls of the fixed frames, characterized in that the method comprises: step 11 of coupling two fixed frames to be arranged in series while a vertical clearance (b) is maintained when the vertical clearance (b) (height difference) is generated between the two fixed frames arranged in series due to a flatness error of a construction surface; step 12 of covering an arrangement gap due to the vertical clearance (b) of opening portions of the fixed frames by continuously coupling the diffusion plate with the two fixed frames; and step 13 of covering an arrangement gap due to the vertical clearance (b) of two side walls of the two fixed frames by coupling the side molds with the fixed frames, whereby the vertical gap (b) between the fixed frames is compensated to be horizontally viewed by a coupling depth adjusted, whereby the arrangement gap between the fixed frames due to the vertical clearance (b) (height difference) of a construction surface is covered with the diffusion plate and the side mold. two fixed frames for the line-type lighting system each having a basic C-shaped cross sectional structure formed with a closing portion, opposite side walls, and an opening portion, wherein a protruding locking portion for guiding fixation of pieces is formed on each inner side of the opposite side walls, and a side mold coupling end is formed at each of the end portions of the opposite side walls; a diffusion plate coupled with the opening portion of the fixed frames; and a side mold formed in an L-shaped or T-shaped cross section, wherein an engaging portion to be coupled with the side mold coupling end is formed on one of the two types of side molds and coupled with each of the end portions of the opposite side walls of the fixed frames, characterized in that the method comprises: step 11 of coupling two fixed frames to be arranged in series while a vertical clearance (b) is maintained when the vertical clearance (b) (height difference) is generated between the two fixed frames arranged in series due to a flatness error of a construction surface; step 12 of covering an arrangement gap due to the vertical clearance (b) of opening portions of the fixed frames by continuously coupling the diffusion plate with the two fixed frames; and step 13 of covering an arrangement gap due to the vertical clearance (b) of two side walls of the two fixed frames by coupling the side molds with the fixed frames, whereby the vertical gap (b) between the fixed frames is compensated to be horizontally viewed by a coupling depth adjusted, step 11 of coupling two fixed frames to be arranged in series while a vertical clearance (b) is maintained when the vertical clearance (b) (height difference) is generated between the two fixed frames arranged in series due to a flatness error of a construction surface; step 12 of covering an arrangement gap due to the vertical clearance (b) of opening portions of the fixed frames by continuously coupling the diffusion plate with the two fixed frames; and step 13 of covering an arrangement gap due to the vertical clearance (b) of two side walls of the two fixed frames by coupling the side molds with the fixed frames, whereby the vertical gap (b) between the fixed frames is compensated to be horizontally viewed by a coupling depth adjusted, whereby the arrangement gap between the fixed frames due to the vertical clearance (b) (height difference) of a construction surface is covered with the diffusion plate and the side mold.