An approach for generating optical frequency comb (OFC) with tunable free spectral range (FSR) is proposed. Two Mach-Zehnder modulators (MZMs) driven by phase-shifted sinusoidal signals are cascaded to generate OFC with plentiful comb lines and the FSR controlled by the drive frequency. Subsequently, a linearly chirped fiber Bragg grating (LCFBG) and a phase modulator (PM) are used to increase the comb FSR by a particular integer multiple. Therefore, by simultaneously controlling the drive frequency of MZMs, the dispersion amount of the LCFBG and the drive signal of the PM, an OFC with desired FSR can be achieved.