Based on single dual drive Mach-Zehnder modulator (DDMZM), a scheme of generating wide and flat tunable optical frequency comb (OFC) is proposed. This scheme has the advantages of simple structure easy to implement, and low cost. A theoretical analysis on the principles of the scheme is conducted and simulation research is carried out with the software Optisystem 7.0. The results show that, as for the generated OFC, although the comb-line number is not big, the flatness is better, and both of its center frequency and line spacing can be tuned independently. The center frequency of the tunable light source determines that of OFC. The comb-line spacing of OFC is obtained by the generated microwave radio-frequency signal based on optical heterodyne method as driving signal of DDMZM, which is up to 150 GHz, and the effective band width is 600 GHz.