Abstract: Nowadays, C4ISR System faces multiple threats and attack measures. Therefore, a method based on encryption lock is proposed to protect C4ISR System. Hardware feature information is written into encryption lock as the key, then make a consistent one-to-one match among each software, each computer and each encryption lock through the world's only serial number of encryption lock. The key algorithm is saved in the encryption lock based on code isolation. And also obfuscated code is used to increase the difculty of software attack. The method has applied in some projects, and the results show that it can e®ectively ensure the safety of the software