The invention relates to the field of communication safety, and especially relates to a call encryption method and device for circuit domain, wherein the method and device are used for solving problems in the prior art that there are many intermediate links in an encryption process and the negotiation process is complex. The method comprises the steps that a first terminal transmits an encrypted call building request to a second terminal based on a user plane; the second user terminal returns a response to the encrypted call building request based on the user plane; the first terminal and thesecond terminal carry out the key negotiation based on the user plane after the first terminal receives the response to the encrypted call building request, and directly carry out the encrypted conversation after the successful negotiation. A calling terminal and a called terminal do not need to obtain secret keys from a network side for completing the encryption of the conversation contents, andcan directly carry out the encrypted conversion without access to the encryption/response interaction, thereby reducing the intermediate links, simplifying the negotiation steps, reducing the time inconstructing the encrypted conversion, improving the encryption efficiency, and improving the user experience.