A secure communication method and device based on application layer for mobile financial service. According to the invention, the exchanged messages in the financial transaction are few, and the requirement for the processing capability of the mobile terminal is low. The invention uses the digital signature technology for information abstract based on asymmetric secret keys, and the integrity of the transaction information is guaranteed and non-repudiation requirement is met. The invention also uses digital envelop technology based on asymmetric secret keys, and the secrecy of the transaction information. The strand space theory proves that the security of the preferred embodiment of the invention can be guaranteed.