Dear Sandip,
As per Gratuity Act refer below definition of continuous service,
Continuous service
(1) an employee shall be said to be in continuous service for a period if employee has, for that period, been in uninterrupted service, including service which may be interrupted on account of sickness, accident, leave, absence from duty without leave, lay-off, strike or a lock-out or cessation of work not due to any fault of the employee.
(2) where an employee (not being an employee employed in a seasonal establishment) is not in continuous service within the meaning of clause (1), for any period of 1 year or 6 months, he shall be deemed to be in continuous service under the employer:
(a) for the said period of 1 year, if the employee during the period of 12 calendar months preceding the date with reference to which calculation is to be made, has actually worked under the employer for not less than 240 days, in any other case;
(b) for the said period of 6 months, if the employee during the period of 6 calendar months preceding the date with reference to which the calculation is to be made, has actually worked under the employer for not less than 120 days, in any other case.