A mixed potential type sensor based on NASICON (sodium super-ionic conductor) was designed for the detection of hydrogen. Two original ways were combined to promote the sensor's sensitivity. LaCrO₃was applied on Au reference electrode as H₂oxidation layer to minimize the H₂response on reference electrode. Additional NASICON layer was coated on Au sensing electrode serving as sensitive electrode for limiting the O₂diffusion. H₂temperature-programmed reduction (TPR) measurement was conducted to test the oxidizability of LaCrO₃. The effect of O₂concentration on sensor's sensitivity was discussed to verify the function of additional NASICON layer. The correlation between the thickness of additional NASICON diffusion layer and sensor's sensitivity was also studied. The research showed that the sensor attached with 0.3 mm thick additional NASICON layer exhibited the largest sensitivity to 100-5000 ppm H₂at 400 degrees C, the slope was -123 mV/decade. In addition, the sensor exhibited excellent selectivity to H₂against the other interference gases, such as CO, NO₂, NH₃, C₇H₈, C₂H₄, CH₂O, C₃H₆O and CH₄.