Abroadband3-dB splitter based on the weighted structure waveguides by the Blackman function is analytically and numerically investigated. The waveguide structure is a symmetric triple-mode evolution structure weighted by the Blackman function to realize the 3-dB splitter with high optical performances. The splitter is analyzed by using the coupled-mode equations and simulated by the use of three-dimensional finite-difference beam propagation method. It is shown the 3-dB splitter is insensitive for wavelength and polarization forever a large bandwidth of 1530 to 1610nm. It is obtained that the power uniformity, wavelength dependent loss, excess loss and polarization dependent loss of the obtained 3-dB splitter within the range from 1530 to 1610nm are better than 2.49×10-3 dB, 0.018 dB, 0.14 dB, and 0.004 dB, respectively. Obviously, 3-dB splitter with high optical performances can be used for C+L-band passive optical network applications.