In thesis, we design a new orthogonal complementary codes- columnwise complementary codes. Its advantage is: (1)As traditional orthogonal complementary codes, it has perfect orthogonal complementary property of auto-correlation and cross-correlation. (2)We can choose different type of columnwise complementary codes to restrain frequency selective fading and time selective fading. (3)Compared with complete complementary codes, it can support more users. (4)The generating method of columnwise complementary codes is easy to understand. (5)It can be used in multi-rate transmission system. (6)The generality: complete complementary codes and 2D OVSF codes are subsets of columnwise complementary codes. We also discuss its bit error rate in a frequency selective Rayleigh fading channel and a time selective fading channel by computer simulation.