Optimization of tillage system for paddy soil requires a precise quantification of soil disturbance, soil structure and tillage energy efficiency. An in-situ tillage test plateform was applied for precise control on the working parameters of a subsoiler, which was a chisel design and was evaluated in five depths (i.e., 10cm, 15cm, 20cm, 25cm and 30cm). Traction, specific resistance, disturbed soil profile and soil fragment distribution were measured to evaluate the performance of the subsoiler. Results showed an increased traction with respect to the engaging depth, which satisfied a secondorder equation. In the 20cm tilling depth the degree of soil disturbance, soil surface humping, soil cracking and longitudinal humping were found the maximum. The bumping height, width, disturbed area of soil profile, mean weight diameter were 16.3cm,42.2cm, 0.0305m2 and 28.77cm, respectively. Specific resistance in this depth was the minimum,i.e. 62kN/m2. When surpassing 20cm depth, the bumping height, width, disturbed soil profile area, mean weight diameter were significantly decreased, which were 10.3cm,31.2cm, 0.0268m2 and 19.12cm, respectively, for the 30cm depth. Compared with the 20cm depth, these parameters were decreased by 36.8%,26.1%,12.1% and 33.54%, respectively. Meanwhile, the specific resistance was 195kN/m2 for the 30cm depth which was increased by 214.5% compared with 20cm depth. In considerating the overall effect of tillage-induced soil struction,soil tilth quality and energy use efficiency, tilling the paddy soil into 20cm provided the best results.