I feel a little pain in my stomach recently. So I want to ask that what is the early symptoms of gastric cancer and how to detect it?

Time to consult with your own medical practitioner.

Stomach cancer is so far down the list of probable reasons for your pain that it makes no sense to waste your worries on it now. Find out if it's one of the very, very common conditions first. The first is gas (heartburn, acid reflux, GERD), relieved by any calcium carbonate such as TUMS, unless it's more in the GERD range. After that, ulcer or gallbladder problems (I had my gallbladder out in day surgery, 3 tiny incisions, very easy). You could be getting sensitive to spicy foods, gassy vegetables, acidic foods, carbonated drinks, chocolate.... so many reasons for stomach pain. You need to be able to tell your doctor exactly where it is, and when it's most likely to happen, because otherwise it's a guessing game for the doctor too. Too soon for expensive tests.

I will agree, where you watching some TV show about cancer or do you have a family history. Perhaps you have a issue with over active worry.

About the last thing on my list to even think about would be cancer, but on cancer, often there is no signs, and you have other issues related, which is caught by medical tests from your doctor

A simple doctor visit can calm your fears, and a Google search can give you more info if you wish, but self diagnosis is both dangerous, since you are not qualified, and an unnecessary stress you inflict on yourself.

Don't get carried away for NOTHING. See a doctor and get the FACTS of your ailment. Seeing a doctor on a regular basis will likely lead to early detection of most serious ailments.

Twice a year, depending on age (Or medical history), or whatever the doctor recommends is sufficient.