The inhibition of tillering by high density is related to the red/far-red ratio (R/FR), while the hormonal mechanism of R/FR regulating tillering in wheat is still unknown. This study aimed to investigate key hormones that mediate the effect of low R/FR on the tillering of wheat and the detailed molecular mechanism. The results showed that low R/FR inhibited the growth of high-position tillers and reduced tiller number. Low R/FR did not alter indole-3-acetic acid (IAA) level, but improved gibberellin 3 (GA3) level and decreased cytokinins (CTKs) levels in the tiller node, resulting in higher IAA/CTKs. The earliest differences in tZ-type cytokinins levels indicated that tZ-type cytokinins were the key hormones, and root application of 6-BA could recover tiller number under low R/FR conditions. The decrease in tZ-type cytokinins levels was mainly associated with up-regulation of cytokinin degradation (TaCKX5, TaCKX11) genes, followed by up-regulation of conjugation (TaCOGT, TaCNGT) genes in the tiller node. Low R/FR almost did not affect IAA metabolism, but induced GA biosynthesis (TaGA20ox1, TaGA3ox2) genes resulting in elevated GA3 level which might further promote CTKs degradation in the tiller node. These results provide new insights into the molecular mechanisms underlying the acclimation of wheat to low R/FR.