In this study, we propose a growth pathaway of scorodite in an atmospheric scorodite synthesis. Scorodite is a non-direct product, which is  derived from the transformation of its precursor, ferrihydrite or poorly crystalline ferric arsenate. Different precursor speciation leads to different crystallinity and morphology of synthesized scorodite. At 10 and 20 g·L^-1 initial arsenic concentration, the precursor of scorodite is identified as ferrihydrite. At 10 g·L^-1 initial arsenic concentrtaion, low arsenic concentrtaion is unfavourable to the complex between arsenate and ferrihydrite, inhibiting the transformation of ferrihydrite into scorodite. The synthesized scorodite is 1-3 μm in size. At 20 g·L^-1 initial arsenic concentration, higher arsenic concentration favours the complex between arsenate and ferrihydrite. The transformation process is accessible. Large scorodite in the particle size of 5-20 μm with excellent crystallinity is obtained. However, the increasing initial arsenic concentration is not always a positive force for the growth of scorodite. When initial arsenic concentrtaion increases to 30 g·L^-1, Fe(O,OH)₆  octahedron preferentially connects to As(O,OH)₄ tetrahedron. Poorly crystalline ferric arsenate rather than ferrihydrite is produced. Even poorly crystalline ferric arsenate can also transform to crystalline scorodite, its transformation process is much slower than ferrihydrite. Therefore, incomplete developed scorodite with poor crystallinity is obtained.