The invention discloses a soft-hard mutation stratum open-cut cable tunnel structure. The structure comprises a cable tunnel sequentially penetrating through a hard soil layer and a sludge layer. An inclined soft-hard stratum boundary is arranged between the hard soil layer and the sludge layer. The structure is characterized in that cement-mixed piles are fixedly arranged at the lower ends of theportions, located in a soft-hard stratum boundary area and a sludge layer area adjacent to the soft-hard stratum boundary area, of the cable tunnel correspondingly; and light solidified sludge and backfill hard soil are backfilled at the upper end of the portion, located in the soft-hard stratum boundary area, of the cable tunnel in sequence. The invention further provides a construction method based on the soft-hard mutation stratum open-cut cable tunnel structure. According to the soft-hard mutation stratum open-cut cable tunnel structure and the construction method based on the same, sludge excavated from the sludge layer on site is utilized for making the light solidified sludge used for backfilling and an impermeable layer, and the construction cost is low; and a soft-hard backfilling soil boundary is in the shape of stair steps and is the same as the soft-hard stratum boundary in inclination direction, the impermeable layer completely wraps settlement joints, and the settlementdifference and mutability are effectively reduced.