A control system of a hybrid electrical vehicle and a control method for a hybrid electrical vehicle are provided. The control system of the hybrid electric vehicle includes: a transmission device (10) connected with wheels (2a and 2b) of the hybrid electrical vehicle; an engine power subsystem (20) connected with the transmission device (10); a motor power subsystem (30) connected with the transmission device (10); and a control module (40) configured to control the hybrid electrical vehicle to operate in a hybrid electrical-economical mode by controlling the engine power subsystem (20) and the motor power subsystem (30), and to control the hybrid electrical vehicle to operate in a first manner if a current slope detected by the hybrid electrical vehicle is less than or equal to a minimum slope and a current electric quantity of a power battery of the motor power subsystem is less than or equal to a first electric quantity threshold, or if the current slope detected by the hybrid electrical vehicle is less than or equal to the minimum slope and a maximum allowable discharge power of the power battery of the motor power subsystem is less than or equal to a first power threshold.