I am a H-1B visa folder, and my wife with H-4 visa can not work now in U.S. I was told the Employment Authorization Document  (EAD). How could my wife get Employment Authorization Document to work in U.S.? 

An Employment Authorization Document  (EAD) is a work authorization document issued by USCIS. The aliens with EAD are allowed to work for any employer in the United States. It is important to understand that the aliens with EAD can work for any employer, and do not need other work visas, such as L1 visa or H-1B visa.

U.S. employers will check the work visa or EAD to make sure all employees are allowed to work in United States. The USCIS Form I-765 is used to file EAD application. To be eligible to receive the Employment Authorization Document, the common way is for an alien to file Form I-485 application after the Form I-140 approval for immigration visa application (Green Card application). 

There are other ways to be eligible to apply for EAD, including L-2 visa holders (spouses of L-1 visa holders), and asylum applicants.