A diversion tunnel blasting excavation back break and out break controlled construction method comprises the steps of judging geological conditions, conducting surveying and setting out; determining the interval of blast holes on the tunnel outline line and conducting marking; drilling holes; feeding explosive into the blast holes; connecting a detonating network; conducting detonating; clearing dangerous rocks, discharging broken bits and the like. By the adoption of the diversion tunnel blasting excavation back break and out break controlled construction method, the smooth control blasting technology is adopted, during blasting excavation construction of a diversion tunnel with complicated geological conditions, rapid lithologic character change, joint fissure development and soft rock occupying the main part, the construction quality can be remarkably improved, the blast hole mark preservation rate of III-type relatively complete rock is 75.8%, the blast hole mark preservation rateof IV-type relatively broken rock is 48.3%, the flatness of the excavation face reaches 90%, the back break amount is effectively controlled, the average radial back break amount of III-type surrounding rock is controlled within 5cm, the average radial back break amount of the IV-type surrounding rock is controlled within 7 cm, the construction quality standard is met, good economic benefits can be achieved, and the diversion tunnel blasting excavation back break and out break controlled construction method provides the reference function for blasting excavation back break and out break controlled construction of similar surrounding rock diversion tunnels in the future.