I'm going to travel with my spouse to the US for visiting. and I want to apply for B1/B2 visa. I filled an application for myself. Do I need to fill a separate DS-160 form for her? If so, how can I link these two applications?
You will need to file separate DS-160 applications for your spouse, but the web site will make this a little easier for you. Once you complete your application, on the "Thank You" page there will be an option to create another application for your family member. When you choose this, it will automatically import some of the information from your form onto the next form, and so it will take less time to complete the second application.
A further explanation is in the DS-160 Frequently Asked Questions:
When you select “Email Confirmation” on your Confirmation Page, you will be directed to a “Thank You” page. On the “Thank You” page you will see an option to create a family or group application. When you select this option, certain information from your application, such as destination, will automatically be imported to and displayed on a new application. Please note that if you use this option you must create an individual application for each family member or for each individual within the group.
If one of the dependents has a different surname or nationality, for example, you can alter that data before submitting the application.
Be careful and make payment for all the applicants at one go; for e.g. if you add/tag your family members or any other member(s) in your scheduling the appointment, then make visa fee for all the applicants at one go in one account. Subsequently, the site does not allow for addition of the same.
I have given this suggestion for addition of this feature on the website itself.