A new color separation method was proposed. Multi-color printer gamut was separated into partitions; every partition was divided into subspaces. Polynomial models were created in subspaces with least square method. Optimal subspace was found first when the targeting colorimetric value was in color separation. Separation result was obtained by solving polynomial equation. The experiment showed that this separation method performs well in accuracy and stability and satisfies the requirement of multi-color high-precision printing.