Then save it at server side,is it possible?
Flash applications can do this, if the user allows them to use the microphone.
You need to use some client technology which can communicate with client hardware(mic), like flash/java(java-i am not that much sure).On the server side you need to implement something like media/streaming server which can record/stream/save client streams.
I done this task using flash on client side and red5 on server side.
I would use a Java applet. The advantage is that you don't have to use any special server-side software like Flash Media Server or Red5. You can process the recorded sound using a simple PHP script - the applet can send a WAV file to the script using the HTTP protocol (something that Flash cannot do, as Adobe wants you to purchase their Flash Media Server).