The degradation of Shandong tobacco-planting soil quality, such as soil compaction and microbial activity reduction, has become more and more serious due to the lack of exogenous organic matter input. Therefore, aiming to improve the soil quality and provide the theoretical support of wheat straw reuse, a two-year field experiment (2016-2017) was performed to study the effect of wheat straw and its biochar on the characteristics of soil physics such as bulk density, field water holding capacity and aggregate stability, as well as soil enzyme activities. Four treatments were set up as follows: chemical fertilizer only (CK), 6.75 t hm^-2 wheat straw plus chemical fertilizer (WS), 2.25 t hm^-2 (FB1) and 4.50 t hm^-2 (FB2) wheat straw-derived biochar plus chemical fertilizer. After two years, the results showed that the WS treatment significantly decreased the soil bulk density (by 14 %) and the fractal dimension (D, by 5.5 %) than that of CK at the 0-20 cm soil layer. In contrast, the content of large aggregate (R_0.25, by 16.53 %), the mean weight diameter (MWD, by 42.53 %) as well as the activities of sucrase, urease and phosphatase (by 112.52 %, 7.81 % and 35.18 %, respectively) were significantly increased (P < 0.05). Compared with CK, the FB1 and FB2 treatments significantly increased MWD (by 27.76 % and 37.5 %, respectively, P < 0.05), however, the soil enzyme activities were changed non-significantly (P > 0.05). Correlation analysis showed that there exists a significant positive correlation between activity of sucrase and MWD and a significant negative correlation between activity of sucrase and D, BD, as well as between activity of phosphatase and D. Overall, compared to biochar, wheat straw is more beneficial to improve soil structure and enzyme activity.