My employer sponsored I-140 based on PERM Labor Certification was approved and my I-485 has been pending for more than 180 days. Due to the employer's business reason, I changed job using the  AC-21 after the 180 day of I-485 pending. 

My new job has a different title, but the same basic duties as the job described in the PERM Labor Certification. Will this affect my pending I-485 application?

The AC-21 determination is governed by duties of the job rather than the job title, as job titles often differ between companies, even for very similar positions. The AC-21 law uses the terminology "same or similar job classification." The duties listed for the original job offer should be compared with the job duties of the new position to determine within which category they fall. 

The DOL categories are generally fairly broad. In many situations, this does not present a significant problem. It is important to note that the duties generally govern, not the specific job title.