Disclosed in the present invention is a large capacity defrosting valve, comprising a valve body; the upper end of the valve body is connected to an upper end cover; the valve body is provided with a piston therein; the piston is connected to a valve core; the upper end of the valve core is connected to a tension spring; the upper end of the tension spring is connected to the lower end of the upper end cover; the lower end of the valve body is connected to a lower end cover; the valve body is provided with a first channel and a second channel thereon; the lower end cover is provided with a third channel thereon; the upper end cover is provided with a fourth channel thereon; a power cavity is formed between the piston and the upper end cover; and a buffer cavity is formed between the piston and the valve body. The present invention has no impact during operation, and has good stability, high reliability and long service lift, thus greatly improving the heating efficiency of an air-conditioner.