A Ge-based phototransistor with programmable characteristics based on the memristor structure was designed and prepared, which consisted of two back-to-back memristors structured with Ni/Ge/GeOx/Al2O3∶HfO2/Pd, sharing the same resistance switch layer GeOx/Al2O3∶HfO2, substrate Ge and bottom electrode Ni. The design of the resistance switch layer was the key to realize the function of phototransistor. The two top electrodes Pd were used as the source-drain electrodes of the phototransistor, and the area between the two memristors was used as the gate of the phototransistor to receive regulation from external illuminant. The electrical and optical response characteristics of a single Ge-based memristor were explored. The output and transfer characteristics of the phototransistor based on gate-control from illuminant were realized. Furthermore, the scientificity and feasibility of this design was verified through exploring the device physics and mechanism. The phototransistor has advantages of non-volatility and compatibility with standard CMOS process, which can effectively simplify the process and reduce fabrication cost. This phototransistor can provide reference for the next-generation of optoelectronic chip to some extent.