Control method of transmission for vehicle and control system for the same

A method of controlling a transmission for a vehicle may include performing deceleration intention determination, by a controller, of determining an intention of a driver for deceleration based on whether a brake pedal signal is received by the controller, upon determining that the driver intends to decelerate, performing downshift determination, by the controller, of determining an intention of the driver to use engine braking based on whether manual downshift of a shifter is performed by the driver, upon determining that the driver intends to use the engine braking, performing continuous shifting determination, by the controller, of determining whether the driver intends to implement maximum engine braking through continuous shifting, and upon determining that the driver has the intention to implement the maximum engine braking, performing continuous shifting, by the controller, of implementing maximum engine braking by shifting to a lowest gear implementable under a current driving condition.