We demonstrate theoretically that the epsilon-near-zero materials can be utilized to control effectively the polarization conversion of an electromagnetic wave through reflection.The significant feature differing from all other means based on whatever natural materials or metamaterials is that for TM incident wave,the reflected phase is a constant,while for TE wave,the reflected phase is a linear function of the incident angle.The phase difference between them covers the range from-180° to 0°,and the polarization conversions from linear states to elliptical or circular states can be obtained by only adjusting the incident angle.Because no complex structures are employed,our proposal promises a simple approach for manipulating polarization conversion at both terahertz and optical frequencies.