The invention relates to a method for open-air deep-hole step pre-cracking hole hole-by-hole detonation pre-cracking blasting cracking in a complex environment, and belongs to the technical field of blasting. According to the method, pre-cracking blasting is carried out along a final boundary line and namely a design contour line of bench blasting, a pre-crack hole should be ahead of a main explosion hole for 100 ms or above to be detonated, a crack is formed through blasting in advance between the main explosion hole and a protected rock mass, after the pre-cracking crack is formed, a bufferhole explosion group and a main hole explosion group are detonated, the pre-cracking crack can reduce the blasting seismic effect of the main hole explosion group, the damage of the surrounding rock mass is slight, the integrity of the rock mass is protected, the workload is reduced, the vibration on surrounding civil houses, cultural relics and other surrounding structures is small, the disturbance on the reserved rock mass is small, the stability is good, the crack forming effect is good, a flat and smooth rock wall surface can be obtained, the overexcavation is greatly reduced, and the stability of surrounding rock is maintained.