Nowadays, lightweight flexible robot is used in many space robots, because these are more transportable and more maneuverable, unlike the rigid-link robot manipulator. However, due to non-minimum phase behavior and distributed link flexure tip-tracking control of FLM is challenging. Also, inherent model uncertainties and environmental disturbance lead to an error in tip-positioning and link vibration. To deal with these challenges, the composite controller is designed. In which, Sliding Mode Observer (SMO) based new estimation law is proposed, to reconstruct uncertain parameter for accurate tip-tracking control of 2-DOF Serial Flexible Link Manipulator (2DSFLM). The Lyapunov theory is used to investigate both convergence and stability of the proposed control system. The performance and robustness of the developed SMO for 2DSFLM is investigated by pursuing simulation studies. It is observed from the simulation studies that the developed composite control scheme effectively estimates the deviation in tip-tracking performance of 2DSFLM with an improved transient response.