The invention discloses a horizontal soil reinforcement method for a subway open-cut foundation pit. The specific steps of the horizontal soil reinforcement method for a subway open-cut foundation pit are as follows: S1: construction of drainage facilities, S2: removal of obstacles at the bottom of the open-cut foundation pit Object, S3: Ramping the foundation pit foundation, S4: Surveying and mapping of the width and depth of the foundation pit, S5: Stock preparation for reinforcing steel bars, S6: Pouring reinforced concrete, S7: Surveying and mapping the reinforced concrete surface formed in the step S6 again, S8: Construction of piles, S9: construction of superstructure, the present invention first constructs drainage facilities, prevents excessive water accumulation, ensures unobstructed foundation pit, reduces construction difficulty, adopts high-pressure jet grouting, high work efficiency, and through vibration The stick removes the residual air bubbles in the concrete in time, improves the quality of concrete pouring, and ensures the reinforcement of the foundation pit. In the surveying and mapping of the width and depth of the foundation pit, at least 3 surveys and mappings are carried out, and the final value is the average value of the 3 surveys to ensure that the surveying and mapping the accuracy of the results.