Abstract:The operations of large integers have been widely used among the fields of public-key encryption algorithms, the operations of floating-point data types of large-scale scientific computation and the construction of large eigenvalues and so on. However, most of the large integer arithmetic algorithms are space and time consuming especially for the large integer multiplication, one of the core large integer operations. When data reaches a certain scale, the overlong serial computing time has been the bottleneck of the applications of the large integer algorithms. Simultaneously, with the popularity of multi-core processors in the computer field in recent years, taking advantages of the parallelism of algorithms, it'll be a trend to parallelize applications to optimize their performance efficiently by using multithread programming to take full use of the powerful computing capability of parallel computers. Meanwhile, the paper did an in-depth study on the multi-core parallelization of fast algorithms of large integer multiplication Comba algorithm and Karatsuba algorithm using the OpenMP multithread programming technology and automatic vectorization technology about the SIMD model of the Intel C++ Compiler. Besides, the testing shows that the speedup of Comba algorithm with 8 threads reaches to 5.85, and Karatsuba algorithm with 8 threads reaches 6.14 at most.