<p>Some organisms using undulatory locomotion show the transition of the swimming frequency and the wavelength of the undulation. This transition of swimming behavior is achieved by sensory feedback, and may have the role to cope with the environmental change. Especially, one of the nematode: Caenorhabditis elegans can modulate its frequency from approximately 0.3 to 2 Hz, and vary the wavelength of undulating body from less than a single body length to almost twice the body length. With this modulation, C. elegans achieves the movement under the conditions from in water to on the surface of an agar. Inspired by this finding, we propose the adaptive control for the multilink swimming robot because the environmental change demands a mobile robot the change of the pattern of the locomotion. Proposed adaptive control employs the sensory feedback from joint angles to inputs of actuators at joints to generate the self-excited oscillation. At first, we construct the multilink model in fluid with sensory feedback. After that, we construct the linearized model to obtain the relationship among the external resistive force, parameters of the multilink model and the swimming frequency by using the eigenvalue analysis. We confirm whether the proposed adaptive control simulates the modulation of undulation like C. elegans. Moreover, we specify parameters of the multilink model which are related to the frequency and wavelength of undulation significantly.</p>