Titanate coupling agents KR-TTS is used to modify nanometer calcium carbonate and the modified powder is characterized. The modification mechanisms of nanometer calcium carbonate is also investigated in this paper. Experiment results show that the optimum conditions of dry modification method as follows: the dosage of KR-TTS titanate coupling agents is 2%, mass ratio of KR-TTS titanate coupling agents to liquid organic solvent is 1:1, modification temperature is 70°C, modification time is 20 minutes, stirring rate is 650rpm. Under the optimum conditions, activity index of modified nanometer calcium carbonate is 100%. The activity index Measurement indicates that modified nanometer calcium carbonate become hydrophobic instead of hydrophilic. IR analysis shows that chemical bonds are formed between titanate coupling agents and nanometer calcium carbonate particles.