Hello Senthil,

Inherit product.product and add field which you want to add.

then inherit the view of purchase order form which is purchase_order_form and then in the tree view of order_line field add your field.

Ex :-

In Py:-

class product.product(models.Model)

     _inherit = 'product.product'

     custom_field = fields.Float('Field Name')

In Xml:-

<record id="inherit_purchase_order_form_view" model="ir.ui.view">

    <field name="name">inherit.purchase.order.form.view</field>

    <field name="model">purchase.order</field>

    <field name="inherit_id" ref="purchase.purchase_order_form"/>

    <field name="arch" type="xml">

        <xpath expr="/form/sheet/notebook/page[1]/field[@name='order_line']/tree/field[@name='name']" position="after">

            <field name="custom_field"/>

         </xpath>

     </field>

</record>

Hope it works for you.

Thanks,