We propose a fiber grating sensor system for condition monitoring of large scale wind turbine blades. A fiber-optic rotary joint was used to transmit optical signals between the fiber grating sensor array and the signal processing unit. Instead of broadband light source, we used a wavelength-swept fiber laser to obtain high output power density. A spectrometer demodulation is used to alleviate the nonlinear wavelength tuning problem of the laser source. For the feasibility test of the proposed sensor system, a down-scaled wind turbine has been constructed and experimented. Fiber grating sensors were attached on the blade surfaces for distributed strain and temperature measurements. With the proposed sensor system we could measure dynamic strain and temperature profiles at multi-positions of rotating wind turbine blades.