A setup for an optical triangular-shaped pulse train with variable symmetry is proposed. The key component is an I/Q (I: in-phase, Q: quadrature phase) modulator. By properly setting the three variables, the optical intensity can be expressed by the sum of infinite sinusoidal harmonics, which indicates the possibility to approximate the asymmetrical waveform. It is found that the scheme is capable for generating an optical triangular-shaped pulse train with a tunable symmetrical coefficient (${20}\% \le \delta \le {80}\% $20%≤δ≤80%) and low fitting error ($\eta \le {6}\% $η≤6%).