We present the first precise determination of the crystal structure for natural canfieldite from the Youqialang lead-silver mine in Nagqu, Tibet, China, using X-ray single-crystal and powder diffraction analysis. The structure was determined and refined to R1 = 0.0375 and wR2 = 0.0986 for a total of 14,743 reflections (2090 independent reflections) with a refined structure formula Ag7.94SnS6, compatible with the empirical formula Ag8.01Sn1.10S6 from electron microprobe analyses. Canfieldite is orthorhombic, with space group Pna21, a = 15.3079(4) Å, b = 7.5549(2) Å, c = 10.7038(3) Å, V = 1237.88(6) Å3 and Z = 4. The structure is composed of isolated SnS4 tetrahedra (average Sn–S bond length of 2.378 Å) arranged in a nearly equidistant manner in three-dimensions with Sn–Sn distances from 7.46 Å to 7.75 Å (the distance along the b-axis is equal to b) and the external S atoms outside the SSn4 tetrahedra are located at the centres surrounded respectively by 6 and 4 SnS4 tetrahedra. The Ag atoms are located in the space between SnS4 tetrahedra and external S atoms in tetrahedral, triangular and linear coordinations respectively with average Ag–S distances of 2.682 Å, 2.554 Å and 2.429 Å. The AgS4 tetrahedra, AgS3 triangles and linear AgS2 share corners and/or edges to form a framework which is corner-connected to SnS4 tetrahedra. Site splitting is present for some Ag atoms with the split distances from 0.26 Å to 0.42 Å. The orthorhombic Pna21 structure of natural canfieldite has similar arrangement of SnS4 tetrahedra and external S atoms to the high temperature cubic F$\bar 4$3m structure, but they are significantly different in the locations and bonding styles of Ag atoms with all the Ag atoms being disordered in the latter. The seven strongest lines of powder X-ray diffraction include [d in Å (I/I0) (h k l)]: 3.240 (45.1) (4 1 1); 3.230 (26.8) (2 0 3); 3.107 (28.1) (4 0 2); 3.084 (100) (0 2 2); 2.724 (49.2) (3 1 3); 2.462 (24) (4 1 3); and 1.895 (54.4) (4 2 4).