The invention discloses a foundation pit support design method. A foundation pit support comprises building envelopes surrounding a foundation pit and an inner support supported between the building envelopes. The design method comprises the following steps that the building envelope in the unit width range is simulated into a foundation beam in the vertical direction, the foundation beam is divided into a plurality of beam units in the vertical direction, foundation soil on the two sides of the building envelope is regarded as a series of soil springs arranged in the vertical direction, and avertical bearing constraint is arranged at the bottom of the building envelope; structure calculation is conducted through the finite element method, the deformation situation of a support structureand the elastic supporting force situation of the soil springs are calculated, according to the load loading manner, along with downward excavation, the soil spring constraint on the excavated side isreleased in the excavated area, and the driving soil pressure load is applied to the non-excavation side; according to a calculation result, the pulled soil spring constraint is released; and operation is conducted again, adjustment and calculation are repeatedly conducted, multi-time model adjustment is conducted according to the building envelope deformation situation and the elastic supportingforce situation of the soil springs till the stress state meets the requirement.