Pectin-Ca microsphere was prepared by sol-gel method with Ca2 as cross-linking agent, and Functional pectin-PDA microsphere adsorbent was modified with dopamine-modified pectin microsphere. The adsorption performance of this adsorbent for removing Th4 was discussed. SEM, FTIR and XPS were used to analyze the preparation and adsorption mechanism.The results showed that the pectin-PDA microsphere had the best effect at pH=3.5. The adsorption capacity of adsorbent reached 37.172 mg/g under the conditions of 25℃, 20 mg/L mass concentration of Th4 , 0.03 g adsorbent, and 1200 min contact time. Co-existing ions Cs , Sr2 , Mn2 and Mg2 had little effect on the adsorption of Th4 . indicating that the adsorbent had better adsorption selectivity;The results of thermodynamics and kinetics showed that the adsorption process conformed to the Langmuir linearisotherm model and the pseudo-second-order kinetics model. The maximum adsorption capacity was 99.010 mg/g. The thermodynamic data showed that the adsorption of Th4 by pectin-PDA was a spontaneous absorption.The thermal stability of pectin-PDA was improved by TG analysis compared to that before modification. The mechanism of adsorption of Th4 by pectin-PDA microsphere was due to the sequestration of N and O on pectin-PDA and Th4 in solution.