The received waveform model for different earth surfaces is significant for altimeter system design, and the model of ocean surface is rarely researched after Tsai. According to the theory of Fresnel diffraction, the character of specular reflection and statistical regularity of the ocean surface profile, the analytic expression of detector output and the average received photons are deduced which are used for ocean altimeter and different from the results of Tsai under the condition of near-normal incidence. The simulated waveform is established for laser altimeter with microradian beam divergence and compared with the real geoscience laser altimeter system (GLAS) received signal. The energy, root mean square (RMS) width, amplitude and shape are very similar and the errors between simulated and real waveforms are all less than 6%. The parameters of received signal are related to the altimeter systems and the wind speed over the ocean surface, and taking the GLAS parameters for example, the valid ocean waveforms can be hardly got when the wind speed exceeds 12 m/s. The analysis and conclusion are important theory basis for the design of laser altimeter system and the wind speed calculation over the ocean surface.