Outdoor baseline is the special length standard in the field of surveying and mapping, it can be used to verify the addition and multiplication constants of the total station and other photoelectric rangefinders. In order to ensure the authenticity, accuracy and reliability of verification results, conducting outdoor baseline traceability periodically is essential. At present, direct measurement by 24 m invar tape or high precision electro-optical measurement is mainly used to achieve the traceability of outdoor baseline in China, a large number of experimental facts have shown that there are still system errors between the quantity transfer of baselines in China and abroad. With the rapid development of China′s manufacturing industry and the proposal of “made in China 2025”, the traditional traceability technology of outdoor baseline is difficult to meet the increasingly high precision requirements, and it is urgent to achieve the outdoor baseline precision ranging. Combined with the current research situation at home and abroad, optical interferometry by Vaisala interference comparator, direct measurement by 24 m invar tape and high precision electro-optical measurement are summarized，the advantages and disadvantages of the three methods are deeply analyzed. Last but not least, some thoughts and suggestions are put forward for the future outdoor baseline field construction in China.