The invention discloses a grooving method and a grooving device for a narrow and shallow engineering pit groove. The grooving method and the grooving device can be used for the grooving of a transversal water drainage pipe of express highway engineering and the construction of other narrow and shallow pit grooves. The efficiency of construction of narrow and shallow pit groove such as traverse water drainage pipe of express highway engineering can be improved. The grooving method is as follows: the pit groove is excavated by the grooving device which goes forward under the drive of a motive power machine, a grooving tool of the grooving device rotates under the drive of the motive power machine, the grooving device comprises the grooving tool, a bracket, a groove depth adjustment lever and a motive power reversing mechanism, wherein the motive power reversing mechanism is mounted on the bracket and meshed with a power-output shaft of the motive power machine, a central rod shaft of the motive power reversing mechanism is connected with the grooving tool, and the narrow and shallow engineering pit groove is grooved by the grooving tool. The grooving device has the advantages that the operation is simple and convenient, the speed is fast, the manual work is saved, the smooth and straight degree of the pit groove can be guaranteed, the excavating quality of the pit groove is improved, the operation is simple and practicable, the groove excavating efficiency is improved remarkably, the labor intensity of workers is reduced, and the engineering construction progress is improved effectively.