The study took the primary saline alkali land in the western of Jilin Province as the research object to investigate the effects of different types and forms of organic materials (granular corn straw, normal corn straw, grass, and sheep manure) on the physical properties and features of water stable aggregates in a primary saline soil by analyzing the immersion bulk density, sedimentation coefficient, field capacity, evaporation rate and quantity, form, failure rate (PAD), water stability coefficient, mean weight soil surface, mean weight diameter (MWD), fractal dimension of soil water stable macro-aggregates and micro-aggregates in the primary saline alkali soil treated with different organic materials in the experimental field. The results showed that: (1) The main components of water stable aggregates were micro-aggregates in each treatment, with the 0.05-0.25 mm micro-aggregates being dominant. The effects of different organic materials on the contents of aggregates of different sizes were significantly different. (2) The stability of soil water-stable aggregates treated with organic materials was better than that of CK. The optimum improvement in MWD was the sheep manure treatment, in which MWD was increased by 104%. The optimum improvement in water stability coefficient and the optimum reduction in PAD was the granular corn straw treatment. (3) The morphology of water stable aggregates was improved by all organic materials, with the granular corn straw treatment showing the best improvement effect, in which the shape of aggregates was round, the surface was rough, and the size distribution was moderate. (4) There were significant differences in fractal dimension of soil aggregates between the granular corn straw treatment and other treatments, but there was no significant difference among other treatments. The fractal dimension of the granular corn straw treatment was the lowest, being 2.62% lower than that of CK. The average mass specific surface area of each organic material treatment was significantly different from that of CK, among which the normal corn straw treatment was the best, which increased the average mass specific surface area by 171.01%. (5) Compared to CK, each organic material treatment had a positive effect on the physical properties of the primary saline alkali soil. Immersion bulk density had a significant positive correlation with PAD and fractal dimension, and had a significant negative correlation with water stability coefficient and average weight diameter. The correlations for settlement coefficient were similar to those of immersion bulk density, but the correlations for field capacity were opposite. Evaporation did not show significant correlation, physical parameters and average mass specific surface area did not show significant correlation. In conclusion, organic materials could improve the primary structure of saline alkali soil, the same organic materials of different forms had different effects; in the present study, the granular corn straw treated with crushing, high temperature and pressure had better effects than other treatments and greatly shortened the improvement time.