A multi-exposures with dose modulation method is presented to fabricate SU-8 mold which is used for microfluidic channels. The method used a maskless digital lithography device with a 405 nm LED source. Digital micromirror device (DMD) maskless lithograph can reach higher precision to meet the requirements of microfluidic chips. For a thick SU-8 layer, multi-exposures with low dose method can effectively suppress the T-shaped structure formed due to top overexposed and bottom underexposed. Two SU-8 molds were fabricated with 55 μm and 25 μm in height in this work. The number of exposures is 62 and 55, respectively. The actual contour of SU-8 structures closely matches the design contour. The PDMS microchannel structure was fabricated using the SU-8 mold. The minimum width of a single microchannel achieved 10 μm. This method provides a more flexible method for fabricating SU-8 molds with higher precision and is well suited for on-chip cell isolation.