In order to reveal the effect of placed angle on flame spread characteristics over polymethyl methacrylate (PMMA), a small-scale flame spread setup was established and then a series of flame spread experiments on PMMA samples with width 3 cm, thick 2 mm and different placed angles were carried out. The results showed that the pyrolysis zone and preheating zone length were largely influenced by placed angle through infrared image analysis. The average flame angle increased greatly when the placed angle changed from 15° to 30° and from ?60° to ?75° (for upward flame spread, the placed angle is positive, and for downward flame spread, the placed angle is negative). Meanwhile, for upward flame spread, the flame length decreased slowly and then increased with placed angle, however, for downward flame spread, the flame length decreased slightly with the absolute value of the placed angle. As for the upward flame spread, when the placed angle changed from 0° to 15°, the average flame spread speed will increase greatly. And for the downward flame spread, the average flame spread speed decreased slightly with the absolute value of the placed angle.