A 4-year field trial was conducted at the Rained Agricultural Experimental Station of Gansu Agricultural University in the Loess Plateau of central Gansu Province. Experimental treatments of carbon (C) addition sources included straw, biochar and no C addition, and each C treatment was combined with three nitrogen (N) addition levels, 0, 50 and 100 kg/hm² respectively. The experimental set-up was a randomized complete block design with three replications. The aim of the study was to determine the effect of different C sources and different N levels on soil bulk density, total porosity, soil saturated hydraulic conductivity, soil aggregate stability and crop yield. The soils were sampled at three layers (0-5, 5-10 and 10-30 cm) per plot. The results showed that compared with no Caddition treatments, application of biochar or straw increased soil total porosity, reduce bulk density, especially biochar addition, it had significant effects on reducing bulk density and increasing soil total porosity at all three observed depths, the effects of straw addition, however, was observed at 0-5 cm layer. Both straw and biochar could significantly improve soil saturated hydraulic conductivity, but the effect of biochar addition was greater than that of straw addition plots. Among observed layers, in comparison with no C addition plots, both biochar addition and straw addition could enhance the amount of soil mechanical stable aggregates and MWD significantly, and the effect of biochar addition was greater than that of straw. The amount of soil water stable aggregates and MWD were increased more significantly in biochar addition soils than those in no C addition and straw addition treatments. Hence, both biochar and straw treated soils improved soil physical properties, and biochar showed the greatest effects. The effects of biochar, straw and nitrogen on crop yield were significant, but biochar was the best, especially biochar 15 t/hm² + nitrogen 100 kg/hm². As a whole, biochar addition was proposed for the sustainable agricultural development in the Loess Plateau of central Gansu Province.