The invention relates to a molten gel back pressure control system and a method for an electrically controlled injection molding machine. The system comprises an embedded controller and a pressure sensor, wherein the pressure sensor is arranged at a gel injection port so as to acquire molten gel back pressure signals; the embedded controller is used for comparing the received molten gel back pressure signals with the preset molten gel back pressure value, so as to obtain the real-time deviation signal; and the embedded controller is further used for performing proportional-integral calculation on the deviation signal, thereby controlling the swiveling speed of a gel injection moor, and the disadvantages that more intermediate sections exist in the normal molten gel back pressure control and the precision is low; as the proportional-integral control is adopted, closed-loop control calculation is directly conducted on the molten gel back pressure acquired by the pressure sensor and the preset molten gel back pressure valve, thereby maintaining constant gel injection pressure; the structure is simple, the parameter is easily adjusted, the dynamic response speed is ensured, and the static error is eliminated; and moreover, no difference degree of the system can be improved, the functions of controlling pressure in real time and accurately controlling the pressure can be realized, and the product quality is greatly improved.