I m a man with 6 foot height but my weight is 52 kg. my diet is normal, how can i improve my weight?

You need a medical c: For your height, you are not health at 52 kg. You should see a doctor to make sure that you do not have a cause for such low weight. There can be malabsorption in your gut or an overactive thyroid gland causing it. In the meantime, you can increase your calories by eating foods rich in calorie such as dairy products- whole milk, ice cream, yogert and meats and eggs.