The requirement of realtimeness and high reliability of data transmission in the WSN based monitoring systems with a long chain treelike topology , the network hotspots problem which is likely to occur around the sink node must be taken into account. This paper proposes a new crosslayer routing algorithm for wireless sensor networks, which is named Cloud model based Multiple Ant Colony routing Optimization (CMACO). Through the interaction of pheromones between populations, the routing algorithm searches for the feasible paths in parallel and updates the pheromones in time. In the pathfinding process, the routing metrics of singlehop delay, hop count, queue length and packet reception rate are regarded as heuristics correction factors. A multiple rules generator is used to optimize the residual factor ρ and the total pheromone information Q so as to update the pheromones adaptively. The simulation results demonstrate that the routing algorithm can guarantee the realtimeness, reliability and robustness of wireless sensor networks. It can also achieve the network load balancing and the congestion control mechanism.