The three-dimensional structure of a natural product, tuguaconitine $(C_{23}H_{35}NO_7)$ from Aconitum sibiricum was determined by single crystal X-ray diffraction analysis. The compound was recrystallized from a methanol solution into orthorhombic crystal system, with a=18.093(4), b=12.075(11), c=9.824(4)${{AA}},;D_m;=;1.35,;D_x;=;1.354;g/cm^3$, space group $P2_12_12_1$, and Z=4. The structure was solved by direct method and refined by least-squares procedure to the final R value of 0.046 for 1495 observed reflections with $I{geq}2{sigma}(I)$. Aconitines are diterpene alkaloid composed of six rings.In the molecule, two 6-membered rings have stable chair conformation, but other two 6-membered rings have unstable boat conformation because of their bonding strain and hydrogen bonds. Based on the three-dimensional structure of tuguaconitine, we suggest another 2D-diagram for the compound which is far better in imagination of the spatial shape of the molecule than the ordinary one.