The invention relates to the technical field of building construction, and discloses a high-low span structure and a construction method thereof. The construction method comprises the following construction processes that after low-span horizontal structure steel bars are bound, structural concrete is poured in the low-span horizontal structure steel bars and guide wall formworks; guide wall construction joints are cleared in a chiseled mode, then wall formworks are supported while vertical structure steel bars are bound, and then vertical structural concrete is poured; after the strength of the vertical structural concrete reaches 1.2 Mpa, structural concrete at the high-low span intersection position is poured in a layered mode; and high-span horizontal structure steel bars are bound, horse stools are arranged, and structural concrete at the position is poured. According to the high-low span structure and the construction method thereof, through the construction mode of layered pouring, operation is easy, the phenomenon of formwork expanding is not prone to occurring, the vertical wall formworks are arranged at the high-low span intersection position, the construction difficultyof the construction technology is lowered while the pouring strength of the high-low span structure is ensured, the quality of the pouring technology is improved, and the construction cost of engineering is lowered.