The development of nanomaterials for biomedical and biotechnology applications is an area of great promise and interest. At present, there are many reports on the toxicity of nanomaterials, which are not unified or even contradictory. It is generally believed that there are two factors causing cytotoxicity of low toxicity nanomaterials. One is when the nanomaterial enters the cell, another is when the nanomaterial overloads on the cell surface. In this paper, a typical low toxicity nanomaterial, nano titanium dioxide, was taken as the research object to investigate the mechanism of cytotoxicity induced low toxicity nanomaterials. The results showed that the overload of nanoparticles on the cell surface destroyed the ion exchange between cell and cell and between cell and medium, which was the key factor inducing cytotoxicity. At high concentration (200 mg/L), the passing rate of nano-TiO₂48h deposited film to Na⁺was inhibited by 60%. In addition, the cytotoxicity evaluation results also showed that nano-TiO₂would produce cytotoxicity at high concentration and long incubation time. Compared with the control group, C_X43 protein expression was increased and distributed more widely after treated with 50 mg/L nano-TiO₂for 48h. This finding provides a general rationale for understanding the cytotoxic mechanisms of low toxicity nanomaterials.