The invention discloses a software upgrading method and system for cluster systems. The method comprises the following steps of: 1, distributing upgrading packages to nodes in a cluster; 2, checking whether the upgrading packages are signed and complete or not; 3, if the checking result is positive, carrying out pre-upgrading operation on the node and preparing to carry out upgrading; 4, if the checking result is negative, forbidding upgrading and returning reasons; and 5, carrying out transaction starting and upgrading on the nodes which undergo the pre-upgrading operation. According to the method, the upgrading package is distributed to each node by adoption of a distribution mechanism so as to carry out independent upgrading, and signature verification is carried out, so that the reliability of the upgrading packages is ensured; and compared with the prior art, the method has the advantages of decreasing the configuration operations need to be realized by system managers, improving the operation and maintenance efficiency, decreasing the operation and maintenance failure possibilities of the system managers and increasing the product reliability.