## 1 Introduction  
The general theory of relativity was developed by [PERSON] in 1915. Gravitational wave theory, which was proposed in the following year, is a corollary to that theory [1]. After decades of continuous exploration, a series of ground-based gravitational wave detection plans were built, including LIGO (Laser Interferometer Gravitational-Wave Observatory) [2, 3], Virgo [4, 5], and Kagra [6, 7]. Third-generation of detectors, such as the ET (Einstein Telescope) [8, 9, 10], were also proposed. Then, in 2015, a gravitational wave was directly observed by LIGO (Laser Interferometer Gravitational-Wave Observatory) for the first time in human history [11], meaning the nature of gravity, cosmology, and astronomy can finally be revealed by gravitational waves. Restricted by gravity-gradient noise and arm length, only gravitational waves with frequencies higher than 10 Hz can be captured by second-generation ground-based detectors. The sensitivity of these detectors is usually \(10^{-23}/\surd\)Hz. With longer arm lengths of 10 km, the detection frequency of the ET is as low as 1 Hz, while the sensitivity is increased by an order of magnitude; however, the frequency range of gravitational waves in nature is from \(10^{-18}\) to \(10^{4}\) Hz [12]. The universe contains a vast number of environmental advantages. The most important are that it contains vacuums, is vibration-free, contains absolute zero temperatures, and is free from ground constraints; thus, space-borne laser interferometers, which can be used to observe low-frequency gravitational waves (\(10^{-3}\)-\(1\) Hz), were proposed, including the LISA (Laser Interferometer Space Antenna) mission [13; 14; 15; 16], Taiji program [17; 18; 19; 20; 21], and Tianqin program [22; 23; 24; 25]. As depicted in Figure 1, the Taiji program was designed to launch three spacecrafts located on the summits of a triangle, whose center orbits around the sun, following the earth at a distance of \(3\times 10^{6}\) km. The triangle forms three arms of the laser interferometer. The detection principle is shown in Figure 2. The working principles for the three triangle arms are basically the same; thus, a single arm between two spacecrafts is used as an example for explanation. Distance fluctuations between two freely suspended test masses are measured by laser interferometry. With the distance fluctuations, gravitational waves can be retrieved. With the three arms, the direction and distance to the gravitational wave sources can be measured [26; 27]. As a key technology in the detection, laser interference is vital to the system. To validate this technology and mitigate its technical risks, a semi-physical simulation test was carried out and is discussed in this paper. To date, several semi-physical laser interference simulation tests have been performed. In the LISA Pathfinder ground test [28; 29; 30; 31], ranging noise of 10 pm/\(\surd\)Hz and angle measurement noise of 10 nrad/\(\surd\)Hz were achieved in a vacuum tank. In order to validate the performance of inter-satellite interferometry ranging in LISA [32; 33; 34], a single laser interference platform was used. Accompanied by a telescope simulator, which was used to simulate the remote spacecraft, a ranging noise of 10 pm/\(\surd\)Hz was achieved. In a pre-study for the Taiji program, an experimental system for precision pointing of the laser link was built in a vacuum tank [35]. The feasibility of DWS (differential wavefront sensing) technology was verified with a pointing jitter of 10 nrad/\(\surd\)Hz. In the Taiji pathfinder mission, an ultraprecise optical bench was constructed in a vacuum tank [36]. The results indicated that a ranging noise of 6 pm/\(\surd\)Hz was achieved. The abovementioned semi-physical simulation tests were focused on technical verification of a single satellite for gravitational wave detection. To the best of our knowledge, there have been no studies focused on the semi-physical simulation testing of inter-satellite laser interference.