In applications of transmission muography for large objects, plastic scintillator strips with triangular or rectangular cross-sections are frequently selected to construct imaging detectors. Triangular scintillator strips have a better position resolution over those of rectangular ones by a factor of ∼ 3.5 with the same width. The big difference has been carefully studied using Geant4. Simulations show a good agreement with those of existing muography instruments. The position resolution is influenced by the geometry (the size and base angle of triangular strips) and the energy resolution of scintillators, and angles of incoming muons. Two empirical formulas have been proposed to quantitatively estimate the position resolution with respect to the abovementioned influential factors. Perpendicularly and randomly (real angular distribution) incoming muons are considered separately in them. A more widely spread angular distribution of muons can make the position resolution worse. For commonly used triangular scintillator strips with a base angle of 45∘, the ratio of the triangle base length to the position resolution is almost fixed to ∼ 12 varying the base length or energy resolution if an uncorrected Centre of Gravity (CoG) method is used. Such a ratio has a potential to be increased by a factor of ∼ 2 if the CoG method is corrected with the muon incoming angle. The influence of the energy resolution on the position resolution can be ignored.