In order to improve the quality of receiving signal for surface nuclear magnetic resonance instrument for groundwater, considering the fact that nuclear magnetic resonance signal is very faint, and often heavily affected by noises and interferences,according to faint signals detection technology, design of low noise circuit and transmission line principle, this thesis focuses on the analysis of matching transmission lines and the preamplifier of the surface nuclear magnetic resonance instrument for groundwater and points out the corresponding solution for noise matching. It gives a design for the cascade order of all blocks of the amplifier from the angle of noise and interference.The performance of NMR(Nuclear Magnetic Resonance) instrument was proved by outdoor experiments, and successfully detect minimum NMR signal at about 470 nV steadily. By adding up more wave signal, we can further reduce noise within signal. The minimum signal we can detect using our nuclear magnetic resonance instrument is 50 nV.