Straw returning is an important technical way to improve soil fertility and crop yield, bearing important practical significance for the sustainable development of agriculture. However, the comprehensive testing and evaluation methods for straw returning quality are still very limited, especially the quantitative description of the spatial distribution of tillage buried straws in soil profile. Taking the performance evaluation on straw returning of rotary tillage as an example, 2D digital image method, 3D reverse engineering technology and Matlab calculation program were used to construct the straw returning quality evaluation and test technology, including composite indicators of the cell, burying rate, depth direction, and horizontal direction. Based on the measure techniques and composite indicators, the spatial distribution of tillage buried straws with six different lengths, i.e. 3cm (T3), 5cm (T5), 7.5cm(T7.5), 10cm (T10), 12.5cm (T12.5) and 15cm (T15) was evaluated and analyzed. In the surface layer, the coefficient of variation of straw proportion in each interval was firstly decreased, and then increased, and finally stabilized, and the coefficient of variation of T5 treatment was 10.2%，which was the smallest. With the increase of straw cutting length, the straw coverage rate was decreased with a logarithmic relationship, and the coefficient of determination of the model was greater than 0.97. In the underground layer, the shorter the length of straw chopped along the depth direction was, the more the proportion of straw in the middle and lower layers (5~15cm) was, and that for T3 and T5 treatments was 76.8% and 71.7%, respectively, which were better than other treatments. Along the horizontal direction, the coefficient of variation of different treatments had no absolute rule, but on the whole, T3 and T5 treatments' horizontal and longitudinal coefficient of variation were not more than 22.8%, and the distribution was uniform. The coefficient of variation of each cell and the proportion of non straw cells were increased gradually with the increase of straw chopping length. The coefficient of variation of T3 and T5 treatments were 73.6% and 73.1%, respectively, and the proportion of non straw cells was 15.7%. Comprehensive analysis showed that straw chopping length had a significant impact on the quality of rotary tillage. T3 and T5 treatments had a better effect on straw mixed burying. Considering the energy consumption, the straw chopping length of 5cm was the best choice for semi feeding harvester.