There is a trade-off between spatial resolution and sensing range of conventional Brillouin optical time domain reflectometry (BOTDR) system. Correlation coded pulses encoding technique has been used to solve this problem. However, when the sampling duration is smaller than the unit pulse width, the restored traces might be distorted by using direct correlation decoded method, thus it will decrease the spatial resolution and accuracy of the system. The influence of the direct correlation based decoded method on the spatial resolution of the system is studied, and a re-sampling based correlation technique is proposed to solve the problem introduced by the direct correlation method. 2 m spatial resolution is achieved over 20 km fiber by using 512 bit 20 ns Golay complementary codes and the new decoded method. The experimental result shows that the proposed decoding method is an effective technique for data processing of coded pulse based BOTDR system.