Are there any convenient bus routes from the downtown Nanjing Road West Area to the HongMei Lu Pedestrian Street?

As far as I know, there are no direct buses to reach that street directly. You have to transfer if you want to take bus, so bus is not suggested.
I am not very clear about your exact position. Generally speaking, it is suggested to take the local subway line 2 from West Nanjing Road Station or Jing'an Temple Station to reach People's Square to change line 10 to reach Longxi Road Station. Get out of the station from Exit 2, you can easily reach Hongmei Road. Walk along that road to reach the Pedestrain Street.