The research was made in fabrication and application of multimode waveguides using the Ag+-Na+ ion-exchange technique in glass. First, Ag+-Na+ ion exchange was run in nitrate melt . Then a electric field was applied. By using this method it is possible to control independently the width and depth of the waveguide. Three-dimensional beam propagation method (3D-BPM) was utilized to simulate and design power splitters with multimode interference (MMI) structure and Y-junction. The measurement results with 1550 nm light showed that the measured loss of multimode straight waveguide can be lower than 0.28 dB/cm, and the insertion loss was 3.6 dB, and uniformity of the splitters was 0.21 dB. It is proved that the fabrication process was adjustable with parameters and reliable on repeatability, which makes it suitable for optical power splitters with high performance.