Legal nature of forestry carbon sequestration transaction in China is introduced. Forestry carbon sequestration transaction is a kind of formal, bilateral, consensual and compensatory legal behavior following the principle of autonomy and having the nature of contract. Legal regulation of forestry carbon sequestration transaction is necessary for making and using demonstration text of contract, distributing the subject right and responsibility of forestry carbon sequestration transaction, offering references for environmental protection and other fields, and developing the voluntary market of forestry carbon sequestration. Based on this, construction of legal system of forestry carbon sequestration transaction is discussed from nine aspects, such as determining the subject, object and the third party in legal relationship of forestry carbon sequestration transaction, making clear the benefit distribution of subjects, and determining the effective element of legal behavior, the transaction price, the performing mode of transaction, the benefit distribution of subjects, the mode of bearing legal responsibility, and the trade dispute settlement means.