Abstract: According to an analysis of planar camber beam under stress,the positive stress on the inner and outer surface of ring during its crushing strength testing has been deducted. The tension stress on the inner surface Caused damage to specimen with a process similar to that during bending testing and σ₊/K value is rebated to the seometric size of the ring R₂/R₁. In case of R₂/R₁=0.87,the σ₊/Kvalue equals to 1.0,i. e. the crushing value K obtained through testing equals to bending strength σ_bb. A modificed formula for bending strenth tested by ring crushing method has also been outlined.