In this paper, the effects of castor oil, BYK22552, polyvinylpyrrolidone (PVP) and TEGO700 on the dispersion of CaOB2O3La2O3 glass/alumina casting slurry of low temperature cofired ceramic (LTCC) were investigated. The rheological properties, thixotropy, solid content and sedimentation properties of the casting slurry were further studied. The dispersion mechanism of four dispersants was researched and explained by infrared spectroscopy. The results show that when the amount of dispersant TEGO700 is 2% of the powder mass, the casting slurry has the minimum viscosity （1 650 mPa·s） and the best thixotropic recovery. Under the optimum viscosity of 2 000 mPa·s for tape casting, the slurry has the maximum solid content （37.2%） and excellent sedimentation performance. The surface of the green tapes is flat and uniform in thickness, and the surface roughness is 144 nm. The surface of the sintered substrate has no obvious defects such as pores and cracks. The sintering densification is improved and the surface roughness is 210 nm. The dielectric constant and dielectric loss of sintered substrate measured at 40 GHz are 6.257 and 1.431×10-3， respectively.