The continuous telecentric zoom lens for a digital light processor (DLP) projector with prisms is presented. The total internal reflection (TIR) prisms between the zoom lens and the digital micromirror device (DMD) are analyzed. To obstruct the false light, it is preferable that the projector zoom lens has a telecentric incident side. To study the structure of telecentric beam path for zoom lens system，the axial displacement equation for the stop was deduced, which keep the system telecentric in all zoom position. A thin lens group fixed with the stop shares the power of the others and makes the cam curve smooth.