can you show us your code? so we can help you 

ok, can you see a field named "Number of Call" value should be -1

or you can do it same with coding like this

<?xml version="1.0" encoding="utf-8"?>
<odoo>
    <record id="ir_cron_your_idname" model="ir.cron">
        <field name="name">any name</field>
        <field name="interval_number">1</field>
        <field name="interval_type">days</field>
        <field name="numbercall">-1</field>
        <field name="doall" eval="False"/>
        <field name="model_id" ref="model_your_model"/>
        <field name="code">model.your_method()</field>
        <field name="state">code</field>
    </record>
</odoo>

Dear Mohit it is a automated action under technical settings. There is no code for it. If you go for technical settings you can create automated action there. While making the new automated action you will find a field called "condition". In that text box I put my condition object.state=="to approve" and it works perfectly except the mail goes twice.