A compact and robust, passively air cooled picosecond 1064 nm Nd:YVO4 oscillator mode-locked by semiconductor saturable absorber mirror (SESAM) is demonstrated. Based on the theoretical analysis and experimental verification of the passive mode locking method, a more precise formula describing the pulse width of a mode locked laser is proposed. The laser operates at pulse duration of 15.5 ps and a repetition rate of 100 MHz with output power of 210 mW. It is proven to be TEM00 mode according to measured beam quality factor of M2=1.15. The root mean square (RMS) power fluctuation is less than 1% . The footprint of the laser is only 350 mm × 150 mm × 50 mm. Thus, this laser can be a reliable seed source to be amplified for more applications in research and industrial fields.