Pd-based constituents have been widely used for sensing H2 due to the incredible selectivity, however, the sensitivity and measuring range in anaerobic ambience are largely limited for these using electronic signals. The variations between Pd and coincided hydride would typically increase resistance upon absorbing H2, whereas the intrinsic α-β phase transition alters the regularity of response features. Surprisingly, an inverse response has been detected by alloying Ag into Pd lattice, and this negative trend could be resulting from a new mechanism based on the experimental investigation and first-principles calculations. It is the contribution of modified Pd/Ag ratio, which optimizes the electronic band structure and density of states (DOS), thus a trade-off between free electron concentration and coincided scattering strength, would tune the response trend and make a switch. Consequently, the resistance of films with proper Ag contents, would be decreased at low H2 concentrations (10 ppm-4 vt.%), and the detection range can be widened as the trend reverses to be positive at high concentrations. These, combined with the ultralow detection limit of 10 ppm, and proportional sensor response values from − 0.5% of 10 ppm H2 to − 3.8% of 4 vt.% at 1 atm, confirm the promising virtues of anaerobic ambience used Pd-based sensors configuring inverse response. Furthermore, our study elucidates that alloying proper elements into Pd to modify the electronic band structure and DOS on Fermi energy, may be an effective strategy for promoting H2 sensing features. Display omitted •Anaerobic ambience used H2 sensors with ultralow detection limit and proportional response are fabricated successfully.•The response trend switch is driven by the balance between free electron concentration and coincided scattering strength.•Baseline drifts of Ag alloyed sensors are suppressed to improve the signal-to-noise ratio.•Experimental investigation and calculations are cooperated to connect the response variation with band structure.