To achieve the selective solid-phase extraction of Pb²⁺ and Hg²⁺ ions by microfluidic chip, the surface modification of nano-silica was carried out by using 3-chloropropyltrimethoxysilane and 5-methylbenzotriazole. And then, an integrated solid-phase extraction chip with replaceable adsorbent was designed and prepared based on the modified nano-silica. The results show that, the agglomeration of the adsorbent is improved significantly. When pH=5, the adsorption rates of Pb²⁺ and Hg²⁺ are 99.1% and 98.9% respectively, while the adsorption rates of Cr³⁺ and Mn²⁺ are only 20.4% and 13.2% respectively. In addition, the absorption rates of Pb²⁺ and Hg²⁺ are both more than 97% even when mixing with the interference ions (K⁺, Na⁺ or Mn²⁺). When the sample flow rate is no more than 1.5 mL/min, the microfluidic chip adsorption rate of Pb²⁺ or Hg²⁺ are both more than 98%; when using the hydrochloric acid (0.5 mol / L) and 2% thiourea [CS (NH₂)₂(W/W)] as eluent, the elution rate of Pb²⁺ or Hg²⁺ is both more than 92% (the flow rate is between 0.2~0.3 mL/min). The successful preparation of selective solid-phase extraction chips for Pb²⁺ and Hg²⁺ contributes to the application and popularization of microfluidic technology in heavy metal pollution monitoring.