To solve the difficulty in ditching for the deep fertilization in tea gardens caused by the high quantity of tea branches and stubbles, a new ditching device combined with a kind of rotary tillage and chisel shovel was designed. The combined ditching device worked by the following steps: Firstly, the stubble, such as fallen leaves and weeds between the rows, was cleaned up and thrown away by the rotary tillage. Then, the chisel-shaped fertilizing shovel forcefully dug into the soil, realizing the deep fertilization groove. The parameters of the rotary tillage and stubble-throwing device and the chisel-shaped fertilizing shovel were optimized by single factor test and quadratic regression orthogonal rotation test, respectively. The optimization results showed that when the number of stubble-throwing blades of the rotary tillage and stubble-throwing device was five, and the blade installation inclination angle was 16°, the stubble removal rate was the highest at the high speed of the cutter (300 r/min), which was 91.64%. When the entry angle of the chisel-shaped fertilizing shovel was 30°, the entry clearance angle was 8°, and the operating speed was 0.7 m/s, the stability coefficient of the groove depth was 94.9%, which was the optimal parameter of the chisel-shaped fertilizing shovel. The field experiment showed that the average width of the ditching was 224 mm (between 202-248 mm), the average depth of the groove was 194.9 mm (between 173-218 mm), and the stability coefficient of the groove depth could reach 92.78%, realizing stable lateral deep fertilization in the tea garden.