Erosion of in-bed tubes and water wall heat transfer surfaces by bed materials and elutriated particles have persistently plagued most fluidized bed combustion (FBC) systems. This paper presents a systematic experimental study of the effects of tube arrangement and flow condition on embedded tube erosion by using erosion-prone acrylic cylinders in a 0.15 m×0.30 m bench-scale cold fluidized bed. The bed material was two different sizes of river sand and anthracite ash with the average diameter of 0.73, 1.24, 0.90 mm, respectively. The static bed height was 0.45 m. Erosion test was performed with the variation of fluidization velocity of 1.2 to 1.8m/s for 100 hours per set. The result shows that the erosion rate increases with fluidizing velocity, with distance from the distributor. The erosion was severe at the tube located in the splash zone of 60 cm above the distributor. The trend with radial direction shows severe erosion at the 4-8 o'clock clockwise compare to other area, especially 5 and 7 o’clock clockwise.