Micro-nano wavelength beam splitter is an important beam-splitting device in photonic chips. In this study, the sequence quadratic program is used to design ultra-compact wavelength beam splitters with footprints of 1.5 μm × 1.5 μm. The Y-type dual channel beam splitter can realize TE/TM mode splitting at the same time, the transmissions of TE mode light at 1140 nm and 1200 nm are 80% and 81%, and the extinction ratios are 18.1 dB and 16.3 dB, respectively. The transmissions of TM mode light are 70% and 67%, and the extinction ratios are 18.3 dB and 15.9 dB, respectively. The T-type beam splitter realizes 180° separation angle splitting, and the transmissions of optical power at the wavelengths of 1100 nm and 1170 nm both reach 88%, and the extinction ratios are 16.6 dB and 15.0 dB, respectively. It is the smallest size chip-integrated wavelength beam splitter. The cross-type three-channel beam splitter realizes splitting with a wavelength interval of 50 nm. The transmissions at the wavelengths of 1100, 1150 and 1200 nm are 73%, 66% and 70%, and the extinction ratios are 17.2, 13.8 and 13.8 dB, respectively. The asymmetric three-channel beam splitter realizes splitting with the wavelength interval of 20 nm. The transmissions at the wavelengths of 1200, 1220 and 1240 nm are 61%, 56% and 57%, and the extinction ratios are 10.8, 7.9 and 8.9 dB, respectively. This method has the advantages of a short design period, high design efficiency, simple structure, easy processing, and suitability for designing chip-integrated photonic components. It is expected that it can provide a new idea for designing chip-integrated photonic devices.