A micro and high-precision fiber Bragg grating soil pressure sensor based on the characteristics of stainless steel patch is developed. Through stainless steel patch and mechanical transfer element, this sensor transfers soil pressure into axial direction tension of the fiber grating and improves its sensitivity greatly. Because of such design, this sensor reduces its volume largely and avoids the chirp effect caused by grating axial stress effectively. The theoretical calculation pressure sensitive coefficient value of this sensor is 29.6557 nm/MPa，which is 9885 times of the bare grating. The performance test proves that the linearity of this sensor is very well and measured pressure sensitive coefficient is 27.5 nm/MPa and slightly less than the theoretical calculation value, which is mainly caused by strain transfer efficiency lower than 1. In order to improve the experimental measurement precision, Haar wavelet transform is used to reduce the instrument error caused by wavelength dithering brought by the limitation of the sample rate and conversion precision of the demodulating equipment. The experiment data show that the dithering amplitudes of grating central wavelength reduce to 50% of the origin data after Haar wavelet transformation.