Considering the imaging restorability, Fisher Information (FI) to evaluate similarity of the point spread functions (PSFs) of different object distances is used to optimize the design of phase mask in practical wavefront coding (WFC) system. A doublet-wavefront coding system is designed based on an infinite focused doublet system with f number 3, effective focal length 100 mm. The simulation and experimental results of encoding and decoding point spread functions show that the doublet-wavefront coding system is insensitive to the object distance with the modulation of point spread function. With object distance from 5 mm to infinite. 3 people (5 m, 10 m, 15 m far a way ) are imaged using traditional doublet and doublet-wavefront coding system respectively. The results show that the sharp imaging's object distance of the doublet-wavefront coding system ranges from 5m to infinite, while the doublet system ranges from 10 m to infinite. In this way the field depth is greatly extended.