According to the requirement for the concentration gradient generator (CGG) in the chip laboratory, a dose-modulated exposure from bottom-up technique was proposed to fabricate SU-8 microstructure. The SU-8 microstructure is used for PDMS CGG. For thick SU-8 photoresist layer, during a one-time exposure, it is easy to over-expose at the top and under-expose at the bottom, which then forms a T-shaped structure. The technique in this article using dose-modulated low power multiple exposure from bottom-up. At last, the photochemical reaction channel inside SU-8 is formed, and SU-8 is fully exposed. This technique effectively suppresses forming the T-shaped structure, and also suppress photoresist liftoff. In this work, after 55 times exposure, a right angle three-level SU-8 CGG structure with a height of 45 μm was fabricated. The width of the single microchannel is 50 μm. The PDMS CGG matches the SU-8 structure. The microchannels are clear with vertical sidewalls.