There are several problems with your formula.
You need to read the Help file for VLOOKUP()
This is the structure or syntax for it:
The first variable (A1 in the formula you posted) is the value you want to find, known as the lookup_value. VLOOKUP is going to try and find the contents of cell A1. Your post showed that cell A1 contained 2001
This means that VLOOKUP is going to try and find 2001 in the table_array.
In the formula you posted the table array was $A$1:$C$1
First of all VLOOKUP is a Vertical lookup, meaning that it looks in a vertical range of cells - cells arranged in columns and tries to find your lookup value in the first column.
Your formula only has one row, and VLOOKUP() will search for 2001 in the first column, which in your case is cell A1
This means that it is looking for 2001 in the cell that contains 2001. It therefor finds it - looking for the contents of cell A1 in cell A1 will always work, but there is no reason to do that.
Your formula has 3 as the index_num, which means that it returns the value from the third column in the table array, which in this case is CLEARK
In summary using VLOOKUP() on a single row is not the usual way that VLOOKUP() is used, and having the lookup value in the same range as the table array does not make sense.
You also say if i apply vlookup in b1 and c1 so this time it work and show correct value
What formula do you have in cells B1 and C1. Again without seeing the formulas it is not possible to know what is going on.
VLOOKUP() is usually used to find if a value in one cell is present in a column of cells (that does not include the original cell). It then returns a value from a column to the right, on the same row that the value was found on.
Here is an example, where I want to know what tool to use for a certain type of product
In cell A1 I put a product name, such as a screw.
In cells in a column C1 to C3 I have the product names including 'screw'
In the next column from D1 to D3, I have the matching tools.
VLOOKUP in cell A2 will show screwdriver when A1 contains screw.
Here it is for nail in A1
A B C D
1 nail screw screwdriver
2 hammer nail hammer
3 nut wrench
The formula in cell A2 is:
As well as telling us what your other formulas are, it would be helpful if you could say what you are trying to do. Someone may be able to advise on a more appropriate formula.
Please remember, as I said before, we cannot see your worksheet, so just saying a formula in cell B1 doesn't work, means nothing because we can't see what the formula is or the data in the cells it refers to.