The photorefractive index generated inside the photorefractive crystal has a very small change and is not easy observed in real time, resulting in the failure to characterize the quality of the writing lattices.In order to observe the temporal and spatial variation of the photorefractive index caused by the writing of photorefractive photonic lattice, we propose amplified Fourier transform method based on Mach-Zehnder optical path. The resolution of the measurement is greatly improved. This method can observe the time and space changes of refractive index of high density photonic lattice in real time, at the same time, it can identify the quality and uniformity of photonic lattice, and solve the time control problem of high density photonic lattice fabrication quality. Compared with the indirect method, the proposed method is more straightforward, the measured data is more accurate and clear, and the resolution can be easily determined by the combination of Fourier transform lens.