## 1 Introduction  
The BeiDou Navigation Satellite System (BDS) is a Global Navigation Satellite System (GNSS) independently constructed by China [1]. BDS combines a variety of satellite constellations and is deployed in three generations [1]. The first generation of BDS consisted of three GEO satellites, which are currently retired. Construction of the regional BeiDou Navigation Satellite System (BDS-2) began in 2004. A total of 20 satellites manufactured by the China Academy of Space Technology (CAST) provide regional services, and 15 satellites are fully operational as of the preparation of this article [2]. In 2009, China began the construction of the global BeiDou Navigation Satellite System (BDS-3). The launch of the final BDS-3 satellite on 23 June 2020 represented the full completion of BDS-3. The BDS-3 constellation consists of 30 satellites, including 24 MEO, 3 IGSO, and 3 GEO satellites. Ten MEO satellites were manufactured by the Shanghai Engineering Center for Microsatellites (SECM), while the other satellites were made by CAST. BDS requires high-quality orbits to support its positioning, navigation, and timing accuracy. In 2012, the Multi-GNSS Experiment (MGEX) was established by the International GNSS Service (IGS) [3] to release precise clock and orbit products through Analysis Centers (ACs) for operational services. Currently, several ACs, including the Deutsches GeoForschungsZentrum (GFZ) [4], the European Space Agency (ESA) [5], the Center for Orbit Determination in Europe (CODE) [6; 7], and Wuhan University (WU) [8] can provide precise clock and orbit products of BDS and other GNSSs. The precise orbit determination (POD) strategies and orbit models are important factors that affect the orbit accuracy of GNSS. However, due to the short construction time of BDS, the POD strategy and orbit dynamic models of BDS are still in the research stage. Thus, the processing strategies and force models of various ACs are still inconsistent at present. Currently, the 3D root mean square (RMS) of MEO and IGSO satellites is approximately 10 and 20 cm [9], respectively, whereas that of GEO satellites is at a meter level. Improving the accuracy of BDS force models requires a thorough investigation of the accuracy performance and systematic errors of existing precise orbit products. One effective approach to validate the accuracy of BDS orbits is satellite laser ranging (SLR), which is an independent observation [10; 11; 12]. SLR offers several advantages, such as a high tracking precision, and is not affected by problems such as phase ambiguities. Therefore, SLR validation is considered a crucial accuracy index for refining BDS orbit modeling [13; 14]. Despite their high accuracy, SLR observations are not entirely free of biases that may contain systematic errors in range measurements. The systematic errors have been identified from the differences among SLR stations tracking LAGEOS [15]. It has also been reported that a systematic error between single-photon and multi-photon stations exists in the SLR observations of GLONASS [16] and Galileo [17]. Previous studies have shown that the relative position between the station and satellite, as well as the quality of the SLR station, can affect the results of SLR residuals, suggesting that the SLR residuals may contain ranging bias. Therefore, evaluating SLR observations is essential before validating the orbits of BDS. This paper validates BDS satellite precise orbit products using SLR observations, focusing on the systematic errors in SLR observations and the non-conservative force modeling effects of BDS orbits. Section 2 provides an overview of SLR tracking of BDS satellites, including laser retroreflector arrays (LRAs) onboard BDS satellites and SLR observations of BDS satellites. Additionally, the method of SLR validation is provided. Section 3 analyzes the systematic effects of SLR ranging related to different types of SLR detectors and different BDS satellites.