Abstract: A nonlinear diagnostic analysis apparatus includes at least one transducer connected to an examinee's head for transmitting a transmission frequency and feeding back a reflection frequency from the examinee's head through the transducer, a detection unit connected to the transducer to allow the transducer to transmit the transmission frequency and receive the reflection frequency, and a control unit connected to the detection unit. The control unit has a computing unit for computing the reflection frequency and comparing the transmission frequency and reflection frequency to obtain detected information, an essential oils database containing essential oils information and essential oils using methods, such that after the computing unit computes the reflection frequency, the detected information and essential oils database are compared to select suitable type and dosage of the essential oil, and a screen for displaying the detected information and the suggested type and using method of the essential oil.