A system for on-line detection of incipient cracks in turbine blades to serve as early warning system for turbine blade failure. The system of non-intrusive detection of turbine blade condition of the invention is simple and cost effective and would enable assessing the health of the turbine blade during plant operation, which is extremely important for the safe operation of the turbine in an operating power plant. The present method and system of identifying the presence of modulated blade passing frequency (BPF,) for blade vibration that is not co-relatable to the change in the operating condition and would thus be indicative of presence of cracked blades with incipient cracking. It is capable for verifying the Campbell diagram and ascertain the margin available between the natural frequency of the blade/stage and the steam excitation frequencies/engine orders.