1. A method for scheduling cloud-computing resource, comprising: receiving a computing request at least including a number of the computing nodes, a start time of computing, and a computing length; retrieving a computing resource table of each of a plurality of computing nodes, wherein the table buffered in a memory of a broker includes a computing pattern obtained from a load history record of each computing node, wherein every load history record is stored in every node's memory; calculating an availability of each computing node according to the computing request and the computing pattern, wherein the availability indicates the available level of the each computing node, and the availability is obtained by summing up values of available resources while any load level of the computing pattern conforms with the computing length; calculating a confidence of each computing node according to the computing request and the computing pattern, wherein the confidence shows the level of how the computing node matches up the computing request, and the confidence is obtained by: calculating a first number of the computing pattern conforming with the computing length and the start time; calculating a second number of the computing pattern conforming with the start time and smaller than the computing length; and the confidence equals to the first number divided by the second number; calculating an expectation value of each computing node and the expectation value equals to the confidence multiplied by the availability; and selecting one or more computing nodes according to the computing request and the expectation value of each computing node; executing a computing task; and distributing the computing task to the selected one or more computing nodes.