In this paper, a kind of electrochemical sensing material with tunable activity and high stability is fabricated from polymolybdate-based metal–organic complex. The polymolybdate-based metal–organic complex: H2Ni(nppa)2(H2O)2[γ-Mo8O26] (1) is synthesized by introducing a flexible pyrazine-pyridine ligand containing amine groups: N-(pyridin-3-yl)pyrazin-2-amine (nppa) under hydrothermal condition. Complex 1 exhibit 1D chain structure based on polyoxoanions and metal ions. The nppa ligands are decorated on the 1D chain in monodentate fashion. Bulk-modified carbon paste electrode (CPE) fabricated by the title complex is used as the working electrode for electrochemically sensing inorganic and organic molecules in aqueous systems. 1-CPE displays electrochemical sensing activity towards BrO3– and ascorbic acid (AA) with low detection limits of 1.22 and 0.76 μM, respectively. Meanwhile, 1-CPE can achieve tunable electrochemical sensing performance, relying on different catalytic activity of reduction products corresponding to multi-step redox reactions. Additionally, its electrochemical activity can be retained under different acid environment.