The invention discloses a novel drilling and blasting construction method for underground engineering in a complex environment. The method comprises the steps of excavating and expanding the working space in the horizontal direction on a working surface, adopting a L-shaped drilling technology to drill a plurality of horizontal long holes in a direction perpendicular to an excavation surface, drilling short holes between the adjacent long holes to achieve the penetration at the bottoms of the holes, sequentially inserting a sawing rope of a rope sawing machine into the adjacent through long holes for cutting, forming a free face between rock bodies to be excavated and surrounding rocks, through multiple cutting, obtaining the outline of a pre-excavation section by penetrating through the free surface, and conducting driving blasting without smooth blasting holes and cut holes on the rock bodies to be excavated. The construction method has fast progress, small vibration and less influence on surrounding buildings, is beneficial for reducing the single consumption of explosives, avoids an over-under-excavation phenomenon, reduces the secondary construction rate, has high efficiency,safety, reliability, economical performance and rationality, provides a better choice for hard rock blasting construction in a complex geological environment, and has great practical value and promotion significance.