In chip-integrated optical circuits, the polarization beam splitter (PBS) is one of the core elements that separates TE/TM modes and transmits them to different ports. We designed an ultracompact Si-based PBS with a footprint of 2  μm  ×  2  μm by an intelligent inverse design method. This method combines the method of moving asymptotes algorithm and the finite element method, and it has a high polarization extinction ratio (PER) and large splitting bandwidth from 850 to 1450 nm. The transmission of the TE and TM modes reaches 93% and 73%, respectively, and the average PER is 21 and 20 dB, respectively. Moreover, we developed other PBSs with different materials and different directional output ports that have wonderful splitting performance in different wavebands.