Aiming at the utilization of the surplus capacity of manufacturing enterprises in cloud manufacturing(CMfg), a job shop scheduling method with idle time is studied. The scheduling framework of job shops in CMfg is built. Including the idle time of processing units, the method of determining processing time series and update strategy of idle time are proposed with the objective to minimize the makespan. A simplify encoding based on jobs and an improved second order particle swarm optimization are adopted to solve jobs' optimal scheduling sequence. Simulation results show the feasibility of the proposed scheduling method. Compared with other algorithms, it is proved that the improved algorithm can get better searching performance.