In order to obtain the deformation and stability characteristics of the uncovered flat geotubes structure under wave action, the wave force exerted on the flat geotubes was analyzed. By introducing a deformation indicator, the geotubes dam stability formula considering the tube deformation was derived in the case of sliding instability and overturning instability. Based on the instability forms and the corresponding deformation parameters obtained from the model test, the effect of deformation on wave force and gravity force in the case of sliding instability and the corresponding torque in the case of overturning instability was discussed respectively. The stability formula considering the geotubes deformation can be further improved if the deformation indicator is calculated. This formula fully considers the geotubes deformation characteristics caused by wave force and it has universal applicability.