The invention provides a technique for producing large-granular aluminium hydroxide or aluminum oxide, which includes the following steps: slurrying, dilution, red mud separation, leaf filtration, seed decomposition, cyclone classification, aluminium hydroxide solid-liquid separation and washing. In the process of seed decomposition, the concentration of aluminum oxide in seminal fluid is 161g/l to 200g/l, the caustic ratio Alpha k of the seminal fluid is 1.35 to 1.65, the seed decomposition time is 40 to 72 hours, the seed ratio is 2 to 3, the first-cell solid content is 400g/l to 800g/l, the first-cell decomposition temperature is 60 DEG C to 80 DEG C, and the decomposed seeds are classified by cyclone based on 60 mum of aluminium hydroxide granules. The invention successfully realizes the stable production of large-granular aluminium hydroxide or aluminum oxide, and while obtaining stable product quality, the invention breaks through the passive situation that the granularity of large-granular aluminium hydroxide or aluminum oxide product is limited at 75 mum for a long time and that the product wear coefficient is limited as 10 percent, thus making a great achievement in terms of aluminium hydroxide or aluminum oxide coarsening.