The invention discloses a concrete viscosity adjusting agent and a preparation method thereof. The concrete viscosity adjusting agent is prepared by copolymerizing a cationic monomer, an anion carboxyl monomer and an inner cross-linking agent together with a free radical, wherein the mole ratio of the cationic monomer to the anion carboxyl monomer and the inner cross-linking agent is 1:(0.5-5):(0.01-0.1). As the cationic monomer and the anion carboxyl monomer are adopted to copolymerize to obtain an amphoteric polymer, the concrete viscosity adjusting agent has remarkable antipolyelectrolyte property and is relatively good in viscosity improvement property; due to adoption of the inner cross-linking agent, three-dimensional net-shaped structures are formed among the viscosity adjusting agent and binding material grains, the concrete disintegration bleeding problem is greatly solved, and the peaceability of concrete is improved. The prepared concrete viscosity adjusting agent is good in compatibility with other additives, the strength development of concrete is not affected, and particularly the concrete disintegration bleeding problem can be effectively solved under the condition of low binding materials.