I installed a bitcoin-qt and received a transaction. Few minutes later, the pc crashed,after restoration of the pc,I only saw an automatic saved wallet.dat file I tried to recover fund but no avail. Please help me to restore my fund
Bitcoin core has keypool option enabled by default, so when you install it a %n of keys will be generated and saved on your PC so when you generate Bitcoin address the address is coming from keypool which is already saved on your PC.
So, Your bitcoins should be on your PC, just give it some time to reindex.
The transactions on the network are kept on the blockchain, off your computer. Your wallet.dat file's main purpose is to remember your private keys so that your wallet program and create transactions and know what addresses it needs to show you as depicting your balance.
Therefore, as long as your wallet.dat file retains your original address information (you can check that by comparing the address that received the transaction to that which you have as a "receiving address") you still have access to your coins. It may just be that your blockchain needs to catch up or the wallet you're using is glitching out at the moment.