The formation mechanism is always a fundamental and confused issue for polyoxometalate chemistry. Two formation mechanisms (M1 and M2) of the Lindqvist anion [W₆O₁₉]²⁻ have been adopted to investigate it's self-assembly reaction pathways at a density functional theory (DFT) level. The potential energy surfaces reveal that both the mechanisms are thermodynamically favorable and overall barrierless at room temperature, but M2 is slightly dominant to M1. The formation of the pentanuclear species [W₅O₁₆]²⁻ and [W₅O₁₅(OH)]⁻ are recognized as the rate-determining steps in the whole assembly polymerization processes. These two steps involve the highest energy barriers with 30.48 kcal mol⁻¹ and 28.90 kcal mol⁻¹, respectively, for M1 and M2. [W₄O₁₃]²⁻ and [W₄O₁₂(OH)]⁻ are proved to be the most stable building blocks. In addition, DFT results reveal that the formation of [W₃O₁₀]²⁻ experiences a lower barrier along the chain channel.