A nanosecond UV laser was utilized to modify the surface of polydimethylsiloxane(PDMS). The experiments were specifically conducted to reveal the effects of laser fluency, spot overlapping and scanning distance on the surface wettability of PDMS. The results show that increasing the laser fluency, spot overlapping or decreasing the scanning distance will make the contact angle of PDMS surface increasing, and all of them are slowly changing to a sharp change process. When the laser fluency is 1.56×10⁶ W/cm², the spot overlapping is 75% and scanning distance is 120 μm, the surface water contact angle reaches the highest 154°. The highest water contact angle can reach 154°. The modified surface was characterized by Fourier transform infrared spectroscopy(FT-IR) and scanning electron microscopy (SEM). It is noted that there are no chemical changes but a micro-nano physical structure formed on the surface after laser process. With Cassie-Baxter model, the mechanism how micro-nano structure affects contact angle is theoretically analyzed.