Considering the factor of system sum bandwidth, two heuristic dynamic spectrum assignment algorithms for open spectrum systems are proposed according to convergency and fairness based on existing ones, they are the fast convergency algorithm with maximum bandwidth (FCMB) and the heuristic fairness algorithm with maximum bandwidth (HFWB). The performance of FCMB and HFWB is compared with the one of the collaboration max-sum-bandwidth (CMSB) algorithm, the randomized distributed (RAND) algorithm and the theoretical max-bandwidth optimal (OPTL) algorithm in system sum bandwidth, fairness and convergency by simulations. Furthermore, the effect of the numbers of primary users, secondary users and channels as well as the radius variance of disturbance area on the performance of those two algorithms is studied. Taking the system sum bandwidth into consideration, experimental results show that FCMB and HFWB outperform other three algorithms in convergency and fairness respectively, particularly FCMB shows superior performance in convergency (more than 300% improved than CMSB while FCMB performs similarly in system throughput).