Ultra-stable lasers are generated by stabilizing their frequencies to the resonances of ultra-stable optical cavities. In order to develop ultra-stable clocks laser for transportable optical clocks, transportable ultra-stable optical cavities need to be developed. Based on the finite element analysis, the vibration-insensitive and structure-robust transportable optical cavity is designed, whose length is 30 cm and it is currently the longest among transportable optical cavities to our best knowledge. The vibration sensitivities of the cavity in three orthogonal directions are measured to be 1.4 × 10 －10 g －1 along the cavity axis (horizontal), 1.5 × 10 －10 g －1 cross the cavity (horizontal), and 1.2 × 10 －10 g －1 cross the cavity (vertical). Compared with normal horizontal-placed optical cavities, the cavity has slightly better vibration sensitivity, and is more robust to be mounted horizontally or vertically. The cavity can be used to develop a transportable optical clock.