hi im mark from philippine but working here in japan my mother have a japanese passport

You have to acquire a tourist visa (L visa) to China, the necessary documents are:
1. your Philippines passport and photocopy of its data pages
2. complete visa application form V.2011A and V.2011B
3. one recent passport photo
4. the Japanese work permit and alien registration card (original and copy)
5. the round-trip air ticket
6. invitation letter from your girlfriend with the copy of her ID card

for marriage in China, first, you have to get a single status certificate from local notary public in the Philippines, second, make it verified by the Regional Trial Court of Philippines, third, authenticated by the Department of Foreign Affairs of Philippines and finally authenticated by the Chinese Embassy/consulate in the Philippines.

what if i have no invitation ?it is okay ?

If you can't provide an original invitation letter from your girlfriend, you need to provide hotel voucher in China besides the round-trip flight tickets.

even i know her address fone no.
that was my only choice the hotel?

Yes, you have to provide the hotel booking even though you know her address.

i*v got a single status certificate given by n.s.o and it was authenticated by phil gov**

should i buy a the round trip air ticket now?
or after i get my visa then i will buy the ticket?

You need to book an air ticket first, use the air ticket booking to apply for China visa, after you get your visa, then pay full payment for the tickets.

As I know, the visa rule for Filipinos are strict, you'd better provide the round-trip ticket booking.