Abstract: By changing crystallization conditions of stirring speed and adding different amount of dispersants (PEG) during catalyst preparation, a series of vanadyl pyrophosphate catalysts were prepared and characterized by XRD, BET and chemical titration to study the effect of crystal structure and micro-morphology on catalytic performance. Experimental results show that stirring speed and dispersant dosage have properly effect both on crystal structure and micro-structure, and the former has a great influence on the average oxidation state of vanadium as well. Appropriate choice of stirring speed and amount of PEG are helpful to achieve a high catalytic performance. Catalytic evaluation results show that at the synthesis conditions of stirring speed 225 r/min, PEG dosage PEG/V2O5=0.10, the n-butane conversion rate of the catalyst is 88 %, selectivity of maleic anhydride is up to 70 % with the yield of 61.7 %.