Continuum robots are robots with high flexibly and maneuverability, which allows use them in confined workspaces with many obstacles. Continuum robot’s motion planning and control are depends on inverse kinematics. Existing inverse kinematics solvers have high computational cost and often fail to find a solution. Moreover inverse kinematics solutions for continuum robots with variable section length underrepresented as well as solutions for multisection robots with mixed sections. This paper presents a further development of FABRIK-based inverse kinematics algorithm that allows operating with multisection continuum robots with variable length. The paper presents analytical solution single section with variable length as well. Our experiments show that proposed algorithm show have higher solution rate and lower solution time in comparison with Jacobian-based inverse kinematics.