The steady intensity of a forward phase conjugate wave (FPCW) is successfully observed along the c-axis in the highly magnesium-doped lithium niobate crystal. We put forward a detailed physical picture for our experiment phenomena. The FPCW is generated from the phase-mismatch in a three-wave coupling process, and tends to be stable accompanied with the building of photorefractive gratings and four-wave coupling processes. Our experimental result is also discussed and analysed by means of the wave coupling theory, and the theoretical expression is provided for the experiment.