The 2, 6-diamino-3, 5-dinitropyrazine-1-oxide (LLM-105) micro-rods with cross section of rectangular were prepared by solvent-induced self-assembly process using nano-LLM-105 as raw materials. And the LLM-105 twin crystal synthesized directly were compared. The effects of solvent, nano-LLM-105 addition, stirring rate and self-assembly time on the crystal morphology of LLM-105 prepared by self-assembly were studied and the possible growth mechanism of rectangular micro-rods was proposed. The morphology, structure, thermal property and purity of crystals prepared by self-assembly were characterized by scanning electron microscopy, X-ray powder diffraction, different scanning calorimetry-thermogravimetry and high performance liquid chromatography. Results show that the regular rectangular micro-rods are assembled under the optimal conditions with dimethylsulfoxide as solvent, nano-LLM-105 addition of 40 g·L^-1, stirring rate of 600 r·min^-1. Comparing to LLM-105 twin crystals synthesized directly, the assembled regular rectangular micro-rods have the same diffraction peaks, but the intensities weaken at 11.1°, 22.3°, 24.8°, and 33.0°, which indicates that the crystal may be preferred to grow in the direction of the (1 0 0), and, its purity was improved by 1.8% to 98.8%. The regular rectangular rod-like crystals exhibit better thermal stability with only one exothermic peak of 356.7 ℃, and the thermo-gravimetric starting temperature(266.3 ℃) improves by 34.8 ℃ compared with 231.5 ℃ of LLM-105 twin crystals.