Tartaric acid, malic acid and ployamines are used as raw materials to synthesize a kind of carboxylic acid amine salt type clay swelling inhibitor and its clay swelling inhibition performance is evaluated through different ways. Experimental results of bentonite linear expansion show that such inhibitor has certain inhibition for bentonite clay hydration expansion. Inhibitory effect of MAA-9 on bentonite is better than that of MAA-1 and TAA-4. When bentonite is marinated in 1.0% MAA-9 solution after 90 minutes, bentonite linear expansion ratio is about the same with that in 4.0% potassium chloride solution, much better than 1.0% potassium chloride solution under the same conditions. Anti-swelling ratio of bentonite marinated in 1.0% MAA-9 solution can reach 66.67% and its anti-swelling experimental results are identical with those of bentonite linear expansion. Other experimental results, such as swelled clay shrinkage experiment, mud ball experiment and drilling fluid property evaluation experiment, further show that MAA-1, TAA-4 and MAA-9 has certain inhibition for bentonite clay hydration expansion.