What subway or bus can I take to the beach from shenzhen shekou walmart area to dameisha beach?

There is no direct subway service leading to that area. You can walk about 0.6 miles to Houhaixincun Station to take the bus J1 to Dameisha Haibin Zongzhan. Then you can reach the beach area for another 0.6 miles walking.

Or you can take a taxi, and the fare is about CNY140.