Accurately measuring wind fields is crucial for weather forecasting, climate and meteorological research, aeronautical flights, and wind resource exploitation. Spaceborne Doppler wind lidar has become an important instrument for observing the vertical profile of the global wind field, with the successful operation of Aeolus. The third generation of FengYun polar-orbiting meteorological satellites is initially designed to develop a dual-system Doppler wind measurement lidar technology program that integrates direct and coherent detection lidar, making full use of the observational advantages of the two methods to detect the global wind field with high resolution. As the first part of a series of simulation demonstration research, this paper presents an end-to-end simulation model for the spaceborne direct detection Doppler lidar system, which is designed to meet the three-dimensional wind detection requirements in the middle and upper troposphere and the lower stratosphere. The simulated spaceborne lidar will work at 355 nm and will deploy the dual-edge detection technique based on parallel-designed Fabry-Pérot filters for frequency discrimination. Referring to the application experience of the Aeolus simulator in demonstration and evaluation, the direct detection lidar simulation model developed in this study can be used to simulate the observation performance of the wind field and develop retrieval algorithms. Moreover, a gridded global atmospheric parameter model is constructed with the usage of the aerosol and carbon detection lidar (ACDL) in-orbit measurements and meteorological reanalysis data to provide as realistic an atmospheric background field as possible for the simulation model. In order to achieve the effective observation of horizontal wind speed and direction, this paper proposes a two-beam stepping detection mode and optimizes the angle design of the observation beam to achieve a better detection response for both the meridional wind component and the zonal wind component. By using this spaceborne dual-beam direct detection lidar global simulation, taking the global wind field simulation at the altitude of 10 km in July 2022 as an example, the modeled horizontal wind speed error is less than 2 m/s, and the wind direction error is less than 8° in most areas.