There are the errors that memory data is not updated, the loop exits early and the loop exits late in the program loop control. In order to ensure the correctness of the program execution in the safety critical system, a new error detection algorithm of program loop control based on ANBD-code (arithmetic-code with signature and timestamp) was proposed. Through ANBD-code, the program variables were encoded as a signed code word by the proposed algorithm. And the errors in the loop control were detected by verifying code signature, the error of memory data being not updated could be detected by using the time label of ANBD-code. In addition, on the basis of the ANBD-code, the errors of the loop exiting early and the loop exiting late could be detected by using the online statement block signature allocation algorithm, the block signature function and the variable signature compensation function. The occurrence probability of an undetected error was 1/ A in theory, where A was coding prime. The primes were selected between 97 and 10993 to test occurrence probability of an undetected error and the Normalized Mean Square Error (NMSE) of theoretical model and test result was about-30 dB. The test results show that the proposed algorithm can effectively detect all kinds of errors in the loop control and the occurrence probability of an undetected error is up to 10 ^-9 when the prime A is close to 2 ³². The proposed algorithm can satisfy the requirements of safety critical system.