I use cash method on my tax return, can i deduct all inventory cost at the same tax year of purchase instead of waiting the inventory is sold. If so, should i use the cost of goods sold form, or deduct them as "Other deductions"

A couple of comments regarding your questions:

• Accrual method of accounting gives you a better picture of your business; in general, no highs or lows
• With the accrual method of accounting, you don't "deduct" inventory.  You track beginning inventory, purchases and ending inventory which then results in CGS.
• If you are eligible to use the cash method and not track inventory, you would deduct the costs (purchases) as noted by @DawnC either as "other expenses" on line 27a of the Schedule C (assuming you are filing this, however, there is no indication of what software you are using), or you can reflect it on Schedule C Part III on line 36.  Using this method you need to also show zero beginning and zero ending inventory.
• This is your 3rd post on this question.