Segwit transaction size not smaller In this transaction;
https://blockchain.info/tx/573700fe19dbc926d037ee67dbe882ebcf3f765f1a3fcc9577665ba40554485f

All of addresses are segwit. According to my research this transaction size must be 166 bytes. But is seems 248 bytes.

Is there any idea?
You are mistaking virtual size that got introduced with SEGWIT with the legacy size.

166 bytes is the virtual size. 248 bytes is the legacy one. Unfortunately, Blockchain.info shows only the legacy size.

You can check your transaction with smartbit to get the VSize.

You can also check this awesome article about SEGWIT fees calculation