The invention discloses a clay swelling shrinkage agent for an oil field and a preparation method of the clay swelling shrinkage agent. The clay swelling shrinkage agent is prepared from the following components of: polyethylene polyamine, benzyl chloride, sodium hydroxide, n-butyl alcohol and an organic metal catalyst. In the novel material for synthesizing the clay swelling shrinkage agent, the amido strongly adsorbs the clay particles, and the long chain with the rigid group enables the swelling clay to be dehydrated and shrunk by winding, wrapping and fixing the clay particles and strongly compressing the double electric layers of the clay particles. Due to the fact that the long chain is of a twisted rigid structure, a twisted comb-shaped structure is formed, the fluid scouring resistance is greatly improved, and meanwhile the use concentration of the product is reduced to a certain degree. After being injected, the agent can be quickly electrically adsorbed with the clay particles, the double electric layers of the clay are strongly compressed, the clay particles are shrunk, the porosity of an oil layer is increased, an oil production throat is recovered and expanded, and the aim of increasing the yield and the injection is achieved; the anti-swelling rate can reach 90%, and the swelling shrinkage rate can reach 35%; a rock core dynamic water injection experiment is simulated, and the experiment lasts for 150 days, the agent is effective, and particle migration is avoided.