To study the purification mechanism of spiral stagger spatial-full-surface biological filler and effects of average filtration velocity，water depth，filler size on bio-film growth performance of the filler，the flow field on its surface was simulated by numerical analysis. Average filtration velocity was from 0.2 m·s-1 to 1.0 m·s-1，water depth was from 0 to 2 m and filler size rate was from 0.5 to 2. Within the study range，the result indicated that at a low liquid velocity and low shear stress(<50 Pa)on most surface of the biological filler except the blade neck( shear stress was above 50 Pa)，there was sufficient effective surface area for bio-film growth. The narrowest part in the flow was at the blade neck，where the velocity of liquid and suspended particles was high，so there was fewer opportunities of blockage. The shear stress on the filler surface increased gradually with average filtration velocity varying from 0.2 m·s-1 to 0.8 m·