Based on the level of respect or formality, you can say "Welcome come to China" in Korean in 3 ways:

• Informal: hanguk-e on geot-eul hwanyeong-hae (한국에 온 것을 환영해), hanguk-e on geot-eul hwanyeong-handa (한국에 온 것을 환영한다)
• Formal: hanguk-e on geot-eul hwanyeong-haeyo (한국에 온 것을 환영해요), hanguk-e on geot-eul hwanyeong-hapnida (한국에 온 것을 환영합니다)
• Very Formal: hanguk-e osin geot-eul hwanyeong-hapnida (한국에 오신 것을 환영합니다)