OBJECTIVE: Elucidating the detoxification mechanism of the raw Pinellia ternata processed by alum solution or alkaline solution (pH > 12). METHOD: Raw Pinellia ternata was immersed in alum solution and alkaline solution according to Chinese pharmacopoeia. Observed the shape's changing of needle-like calcium oxalate crystals by scanning electro-microscopy. Determinating the contents of calcium oxalate crystals by applying oxidation reduction titration. Measured the irritations of raw P. ternata and various processing products on the model of rabbits'eyes. RESULT: After processed by 8% alum solution prescribed in Chinese pharmacopoeia or 10% sodium carbonate solution, the needle-like shape of raphides in raw Pinellia ternata were changing and the sting barb of raphides were rusted and dissolved, the contents of calcium oxalate crystal in raw Pinellia ternata were sharply declined from more than 1% to less than 0.5%. the decline of contents is relative to the irritation decline of P. ternata on rabbit's eyes. Less than 0.5% calcium oxalate crystals of P. ternata almost had no irritation. CONCLUSION: After processed by 8% alum solution or sodium carbonate solution (pH > 12) , the irritation components in raw P. ternata could be rusted and dissolved, the needle point of raphides was broken, which led to the raphides'content declining and the irritation disappearing. The micro-structures, shapes and contents of calcium oxalate crystals in different medicine plants were not same. These properties of calcium oxalate crystal in India Madder Root and yam et al were very different from those in raw P. ternata.