<p>Strain engineering has emerged as a powerful strategy to modulate catalytic activity, yet its general applicability remains uncertain, especially for magnetic catalysts where spin effect also plays a critical role in governing reactivity. Here, we reveal a metal-dependent modulation on adsorbate chemisorption to strain, with magnetic metals exhibiting reduced strain sensitivity compared to non-magnetic metals. Using ammonia synthesis as a model reaction, we attribute this behavior to an antagonistic interaction between strain and spin, wherein spin effect counteracts strain-induced chemisorption modulation and becomes stronger with increasing magnetism, originating from the varying shift of d-band center under the combined effects. Kinetic analysis further confirms that strain engineering markedly modulates the reactivity of weakly magnetic or non-magnetic metals by reshaping traditional scaling relations under strain-free conditions, while offering marginal impact to strongly magnetic metals. Accordingly, we propose a practical strain-based strategy to enhance the activity of representative ammonia synthesis catalysts, including Fe, Co, Ni and Ru. Moreover, the metal-dependent strain effect can be extended to key intermediates in other reactions, indicating a general phenomenon and establishing a conditional principle for applying strain engineering in metal catalysts design.</p>