The invention discloses a construction method for excavating a weak surrounding rock tunnel by a hydraulic breaking hammer. The construction method comprises upper pilot tunnel excavation, deslagging, primary supporting, lower left pilot tunnel excavation, deslagging, primary supporting, lower right pilot tunnel excavation, shortcut backfilling, primary supporting, inverted arch and cavern excavation, deslagging, and construction of inverted arches, filling, small sidewalls, secondary lining and the like. The construction method adopts dynamic monitoring, performs scientific construction organization, avoids blasting explosive use, generates small amount of dust, has superhigh adaptability and good control performance for overexcavation and under-excavation, is small in surrounding rock disturbance, and is high in lining and building quality, stability, reliability and security degree; and mechanical characteristics of the surrounding rock are closer to a design condition.