The application background and techniques to generate sawtooth wave based on photonic approaches are introduced. To overcome the electronic bottleneck of electronic waveform generation methods, we propose a novel method to generate sawtooth waveforms by using two parallel Mach-Zehnder modulators (MZMs) based on external modulation. We adjust the voltage of the direct current source and the intensity of the radio frequency source in order to make MZMs to operate under conditions of quadrature transmission point (QTP) and proper modulation index. Thus, the frequency components′characteristics of the photocurrent from optoelectronic balance diode are coincident with the Fourier series of sawtooth. A mathematical model is built, and the scheme is verified experimentally. The root mean square error is used to evaluate the simulated and experimental results. In addition. The influences of the extinction ratio and the drift voltage on the output signal are analyzed. The results show that the proposed system is flexible and has strong scalability. The waveform generation and slope switching can be realized through simple actions.