A communication apparatus and its setting method are provided. The communication apparatus has a processor and a memory device storing a short message receiving module configured to, when executed by the processor, determine whether the short message received by the communication apparatus conforms with a predetermined format. The short message includes an unencrypted prefix and multiple encrypted fields including a device serial number of the communication apparatus, a time at which the short message is sent and an operation command that controls the communication apparatus to execute a corresponding operation. The short message received by the communication apparatus is decoded to obtain the operation command when the short message conforms with the predetermined format. The operation command controls the communication apparatus to execute the corresponding operation, and the predetermined format includes at least an unencrypted field and at least an encrypted field.