Based on cascaded phase modulators (PM), a scheme to generate a optical frequency comb (OFC) with adjustable comb number and comb spacing is proposed and experimentally demonstrated. The sinusoidal radio frequency (RF) signal and its double-frequency signal are used to drive the two cascaded PMs, respectively, simultaneously a small frequency offset is introduced in the second RF signal, and finally a phase-insensitive and high flatness OFC is obtained. The comb number and flatness are regulated by the modulation index of these two cascaded PMs. When the frequency offset is 10 -5 times the frequency of the second RF signal, the flatness of this OFC is less than 3 dB. The experimental results show that the comb numbers are 7, 9, and 11, the comb spacing is 5.5 GHz and 7.5 GHz, and the flatness is smaller than 2.4 dB for the generated OFC.