The type and dosage of dispersant, resin and wetting agent directly affect the dispersion and stability of pigment particles and the construction of thixotropic system in pigment gel ink system. The rheological behavior of pigment slurry with different amount of dispersant BYK–191, and gel ink with different quantities of styrene acrylic resin M101 and wetting agent 4187 was investigated. The particle size of pigment, microscopic imaging, CMC (critical micelle concentration) were studied by laser particle analyzer, optical microscope and surface tensiometer. Besides, it was the first time to use rheometer to optimize the gel ink formula. It turned out that not only a well thixotropic system of gel ink but also the ultra-fine dispersion and long-term stability of pigment could be realized when the adding quantity（mass fraction）of dispersant BYK–191, styrene acrylic resin M101 and wetting agent 4187 reached 2.0%, 4.0% and 2.5%, respectively.