The fibre pullout test was conducted to investigate the influence of the water stability on the bond behaviour between the Magnesium phosphate cement (MPC) matrix and the steel fibre. The composition of the MPC-matrix and the immersion age of the specimens are experimentally investigated. The average bond strength and the pullout energy are investigated by analysing the experimental results. In addition, the microscopic characteristics of the interface transition zone are investigated using scanning electron microscopy (SEM). The experimental results showed that the bond performance between the MPC-matrix and the steel fibre decreased significantly with the increase of the duration of immersion in water. The average bond strength between the steel fibre and the MPC-matrix reduced by more than 50% when the specimens were immersed in the water for 28 days. The effect of the water on the interface between the steel fibre and the MPC-matrix was found to be more significant compared to the composition of the MPC-matrix. In addition, the MgO-KH2PO4 mole ratio of the MPC significantly influenced the water stability of the interface zone between the steel fibre and MPC-matrix.