Modulation of anatase toward highly active facets has been attracting much attention, but the mechanism and photoactivity are still ambiguous. Here we demonstrate the inherent mechanisms for facets nucleation and morphology evolution, and clarify some vital influences of facets and surface nature on the photoactivity. Simply tuning the Ti/F ratio in the synthetic mixture leads to single anatase crystal exposed with different facets like {001}, {010}, or {110}. And complex sphere structure exposed with {001} facets can be formed by secondary nucleation and growth. Prolonging the hydrothermal treatment time causes selective etching on {001} facets, whereas defluorination via thermal calcination produces many pores on the surface. The photodegradation of positively and negatively charged, and zwitterionic dyes indicates that the type of reactant, adsorption mode and surface area play significant roles in photocatalysis. This work makes a step toward understanding the formation of facet-mediated structure and designing highly active materials for environmental remediation, hydrogen production, and dye-sensitized solar cells.