In order to remedy some defects in a traditional handy system for measuring the crack width in a concrete structure ,such as the difficulty inaccuracy focusing and the blur image due to the small focus depth and aberrations, a new system based on a wave-front coding was designed to extend the focus depth.The normalized parameters of a cubic phase plate and the relationship between these parameters and their corresponding real design parameters were discussed. Then a handy measurement system based on the wavefront coding with CODE V was designed. Finally, the cubic phase plate was fibricated and a preliminary experiment was carried out. Experimental results indicate that the field depth of the wavefront coding system based on a single lens can be extended to 15 mm when the resolving power is 50 μm and the F number is 6, which is 4.5 times as deep as that of traditional optical systems in theory at the same F number. The system can satisfy the requirements of extending focus depth and imaging in measuring the crack width of a concrete structure.