The optical characteristics of the Y-beam splitter based on polyst yrene (PS) microwires are investigated. It is found that the light splitting ratio can be adjusted by changing the c oupling length between the two arms of the splitter.The effect of transmission loss and surface scattering loss of the component on the optical characteristic is discussed as well.It is shown that,the transmission loss of a 1.5-μm-diame ter PS micr owire is 0.0108dB/μm at the wavelength of 650nm;in the Y-beam splitter,the transmission loss of PS microwire can be neglected,while the scattering loss of the same PS microwire has a great effect on its optical characteristics,w hich shows the potential application in suspended particles sensing based on PS microwire.