To provide a method for producing easily a GI type plastic optical fiber preform adjusted precisely refractive index distribution.

The manufacturing method of GI type plastic optical fiber preform includes that the polymerization is performed injecting monomer source material into a rotary tube for optical fiber preform production, after forming a cladding part which has the fixed refractive index in the direction of the center from the wall surface of the tube, the polymerization is performed changing and injecting composition of the monomer source material gradually, so that the raw material with the high refractive index may be included so much, and the core part which has the refractive index gradually increased from the boundary face with the cladding part to the core, is formed continuously.