why the pool difficulty is constant 32?
I believe you are referring to the active miners mate , current difficulty is

{
"blocks" : 796,
"currentblocksize" : 1000,
"currentblocktx" : 0,
"difficulty" : 1.65237891,
"errors" : "",
"generate" : false,
"genproclimit" : -1,
"hashespersec" : 0,
"networkhashps" : 73486030,
"pooledtx" : 0,
"testnet" : false
}