Well, because of Great China Firewall the vast majority of file sharing services do not work in Mainland China.
A lot of users in China opt to use VPNs (virtual private network) to access all the platforms that are blocked by Firewall. VPNs use encryption and security protocols, so it is not publicly visible what services are you using via VPN. However the China’s government is constantly blocking these VPNs, and they are being shut down every now and then. From January 2017 China's Great Firewall is doubling up on VPN regulation, and Chinese government has tightened their grip on internet use in the country through a 14-month long campaign that will target the use of virtual private networks (VPNs) and other "illegal" internet.
That’s why I see you are looking for a file sharing platform that works across the Firewall. I work for Maytech, secure data transfer and storage company, we offer two online storages that work in China, both of them are registered on G-Cloud and accredited by the Cabinet Office for confidential data up to Official Sensitive: Quatrix and FTP Stream.
Quatrix - easy to deploy, easy to use, yet provides strong encryption both at rest and in transit, granular permissions, and a full audit trail.Quatrix provides pin protection for share; 2FA for user login, Outlook integration; secure connection over HTTPS and SFTP; PGP module; customization and branding.
FTP Stream China - a hosted ftp data transfer platform that enables you to rapidly send and receive files to China of any size securely and with no bandwidth limits; total site branding; HTTPS, FTP, SFTP transfer protocols; full logging and tracking for compliance; embed file transfer right into your website.