In order to reduce measuremental errors of fiber Bragg grating (FBG) wavelengths resulted from the driving element of tunable Fabry- Perot (F- P) filter, which has the characteristics of temperature drift and nonlinearity, an improved dynamic real-time calibration approach is proposed after analyzing and comparing two kinds of real-time correction systems respectively with series and parallel structures. Then the real-time correction system with improved concatenation structure is investigated. The reference grating module with good thermal stability is designed to guarantee that wavelengths of four reference FBGs in the module keep constant for a long time. An accurate resistance temperature detector (RTD) is integrated into the model and clung to the reference FBGs. Before measurement, the correlation between the wavelengths of four reference FBGs and temperatures measured by RTD is calibrated. By reference points provided by referenced FBGs, the function between transmission wavelength and driving voltage of tunable F-P filter is adjusted in real time during every scanning period. The experimental results demonstrate that the maximum error is ±3 pm using the improved dynamic realtime calibration method to demodulate wavelengths of FBGs. Compared with the method to determine center wavelengths by direct acquiring driving voltages, the accuracy is enhanced 6 times. Compared with the reported method using series structure, the accuracy raises 3 times.