I'll fly from Guangzhou to Sanya for 6 days. May I leave luggage at Baiyun Airport for this time?

Yes, you can leave your luggage at CAN. There are 6 Left Luggage Counters at the airport: one beside Gate 16 in Domestic Baggage Claim Lobby; one beside Gate-8 in International Departure Lobby, two in Domestic Arrival Area B, and two in International Arrival Area. You may dial at 86-020-36066859 to consult the staff about the price. Good luck to you! :)