A construction method for foundation pit enclosure and earth excavation, comprising the following steps of: construction drawing design and drawing review, construction site preparation, support enclosure arrangement, drainage measure arrangement, earth excavation, cushion layer, bottom plate and force transmission belt pouring, support dismantling, basement structure construction completion, earth backfilling, and grouting after pile pulling. Foundation reinforcement measures in a pit are used, and accumulated water in the foundation pit is pumped out in time, such that in the whole pit digging process, the foundation pit has better stability, meanwhile, excavation is performed in sequence in a segmented and layered mode from top to bottom, the gradient is reasonably controlled, slope toe cutting is avoided, side slope instability is prevented, and the safety is better.