A digitally controlled non-inverting buck-boost DC-DC converter system including a non-inverting buck-boost DC-to-DC converter control module and a negative feedback module and applicable for a radio frequency circuit module is revealed. By locking a duty cycle to two specific levels, the non-inverting buck-boost DC-to-DC converter control module only needs a single operation mode to achieve the required effects. Simultaneously, pulse-skipping phenomenon is also avoided. Furthermore, a reference voltage is modified through a reference voltage correction circuit of the negative feedback module to eliminate errors between previous DC output voltage and the reference voltage. Thereby the DC output voltage can remain in a stable state so as to reduce operational defects during the mode transition.