Optimization experiments were carried out for preparation of a catalyst precursor. Results show that the acid concentration and reaction temperature in precursor preparation exhibit strong effects on the catalyst behavior. For the catalysts prepared at higher concentrations of acid, the quantity of the V4+ phase (VO)2P2O7 is large, and the n-butane conversions are all quite high. When decreasing the acid concentration in precursor preparation, the relative amount of the V5+ phase δ-VOPO4 and the n-butane conversion increase continuously; at the same time, the selectivity to maleic anhydride increases at the beginning, and then decreases after reaching a maximum value. The catalyst prepared at an acid concentration of 102.3% gave a maximum yield of maleic anhydride of 48.10% at an inlet n-butane concentration of 4.0% and a space velocity of 500 h−1. The fine particle catalyst in this study offers great flexibility of operation.