SFTP (SSH File Transfer Protocol) transfer speed is affected by a number of factors, including but not limited to the following:

Network Bandwidth: Network bandwidth is one of the main factors limiting SFTP transfer speed. If the network bandwidth is limited, then the data transfer speed will be restricted.

Server Performance: SFTP transfer speed is also affected by server performance. If the server's processing power is insufficient, then the data transfer speed may be slowed down.

File Size and Volume: Transferring a large number of small files may affect SFTP transfer speed as each file needs to be processed separately.

Encryption Algorithms: SFTP uses encryption algorithms to secure data transfers. However, these encryption algorithms may have some impact on the transfer speed, especially under high strength encryption algorithms.

Data Compression: In order to improve the efficiency of data transfer, some SFTP clients support data compression. However, compressing and decompressing data may consume the server's processing power, thus affecting the transmission speed.

Path length and name: In some cases, the path length and name in the file system may affect the SFTP transfer speed.

In order to improve the transfer speed of SFTP, some optimization measures can be taken, such as:

Choose a high-speed Internet connection: Choose a high-speed Internet connection as much as possible to increase the network bandwidth.

Optimize server configuration: Optimize the configuration of the server to increase its processing power.

Use file compression: Use file compression on the client side to reduce the amount of data that needs to be transmitted.

Choose appropriate encryption algorithms: Choose appropriate encryption algorithms according to the actual situation in order to balance transmission speed and security.

Optimize the file system: Optimize the path length and name of the file system to reduce transmission time.