Beam spreading is an important effect when a beam propagates in atmospheric turbulence. The collimated Gaussian beam spreading experiments are carried out with beam dynamic change test system under the sea surface environment in Yantai region, and the beam spreading characteristics are analyzed based on data including beam spreading, temperature, relative humidity and atmospheric refractive index structure parameter in different distances and different time periods experiments. Results show that the correlation between beam spreading and refractive index structure parameter is better in sunny weather than in stormy waves weather. But in stormy waves weather the correlation between beam spreading and temperature and relative humidity is good at certain time. In the condition of the same link distance, the beam spreading is obviously smaller at night than in day, and the amplitude fluctuation of beam spreading has the same results.