Focusing on the safety analysis of the 3D block cipher, a new method on this algorithm against the meet-in-the-middle attack was proposed. Based on the structure of the 3D algorithm and the differential properties of the S-box, the research reduced the number of required bytes during structuring the multiple sets in this attack and constructed a new 6-round meet-in-the-middle distinguisher. According to extending the distinguisher 2-round forward and 3-round backward, an 11-round meet-in-the-middle attack of the 3D algorithm was finally achieved. The experimental results show that:the number of required bytes on constructed the distinguisher is 42, the attack requires a data complexity of about 2⁴⁹⁷ chosen plaintexts, a time complexity of about 2^325.3 11-round 3D algorithm encryption and a memory complexity of about 2³⁴² bytes. The new attack shows that the 11-round of the 3D algorithm is not immune to the meet-in-the-middle attack.