Abstract: To do further analysis of the security of lightweight block cipher TWIS, 3-subset meet-in-the-middle attack was applied to 10-round TWIS without the final whitening. Based on the weakness in the key schedule of TWIS：its actual key size was only 62-bit and the confusion speed of the initial key was rather slow, the time complexity to recover the whole 62-bit key of 10-round TWIS was 245, and the data complexity was low enough with only one known plaintext-ciphertext pair. The result shows that block cipher TWIS is not secure under 3-subset meet-in-the-middle attack.