The relationship between the bending strength and the size of Chinese larch visually-graded lumber was investigated. 1,961 pieces of lumber with three different widths were divided into two groups of high visual grades and low visual grades. The ultimate bending strength was tested under test spans of 18 times test depths. The combined length and width size effects of 5th percentile of bending strength were estimated by the slope method and the parametric method. Using the slope method, the estimated effect parameters of H and L were 0.19 and 0.23 for the 5th percentile.