About maximum clients

[nanaruru12]

is there a maximum number of clients(users) access to splunk server at the same time??

then what about default number?

[alacercogitatus]

The number of end-users allowed to access the Splunk Searchhead is based on Hardware specifications and Internal Policy at your company.

You should review the sizing guide.
http://docs.splunk.com/Documentation/Splunk/6.2.0/Capacity/Referencehardware