An iris acquiring optical system with wavefront coding technique was designed, which can increase the depth of the field and get image at natural state without restriction. By applying the conventional imaging evaluation metric, Strehl ratio and encircled energy were used as the imaging features, and the wavefront coding system was design with ZEMAX, then a better trade-off between insensibility to defocus and restorability was obtained. The depths of focus of the system with cubic phase mask and modified cubic phase mask and the conventional system were compared. The result suggests the depth of focus of the iris acquiring system with cubic phase mask is the best which can attain by a factor of 8 over conventional iris acquiring system. The design increases the distance of the iris acquiring which has some reference value to the design of the iris image acquiring system at natural state.