The paper under review is to prove that if \(\widehat{HFK}(Y, K, [F], g(F)) \cong \mathbb Z\) then \(K\) is fibred and \(F\) is a fibre of the fibration, where \(K\) is a null-homologous knot in a closed connected oriented 3-manifold \(Y\) with \(Y - K\) irreducible, \(F\) is a genus \(g\) Seifert surface of the knot \(K\). This result was a conjecture by Ozsváth and Szabó. The author briefly reviews the sutured manifold introduced by Gabai and a sutured manifold invariant in terms of the knot Floer homology in section 2. In section 3, the homological version of the main result Proposition 3.1 is proved for the sutured manifold obtainded by cutting \(Y - int(Nd(K))\) open along the Seifert surface \(F\). The horizontal decomposition formula for the knot Floer homology is given in section 4. The main technical constructions on relative Morse function, curves in sutured manifolds, Heegaard diagrams and the product decomposition formula are given in section 5 and Theorem 5.1. Section 6 contains Ghiggini’s strategy along with Gabai’s method. The main theorem of the paper is proved in the last section 7. An interesting Remark 1.5 is to point out that there may be a mysterious relation between the knot Floer homology and the fundamental group by the Stallings’ fibration theorem.