Mr.Cindy, You can apply for L visa for visiting your friend, normally the duration of stay of a "L" visa is 30 days, which means the holder of the visa may stay in China for up to 30 days from the date of entry. If your estimated stay in China is longer than 30 days, please make it clear in the application form and ask for the Visa Officer's approval when you submit your application. You can write that you want to stay in China for 180 days on the Item "Your Longest Intended Stay in China" on the visa application form. Maybe you will get a single-entry L visa permits 180 days stay duration. You can also apply for 6 months double-entry visa with 90 days stay per entry.