1. A remote monitoring system for remotely monitoring execution status of a Programmable Logic controller (PLC) program of a machine, comprising: a storage module, storing ladder diagram information corresponding to a PLC source program of the machine, wherein the ladder diagram information includes a PLC signal address relation information, a plurality of logic switches and a responsive collect command of each logic switch of a ladder diagram, and the PLC signal address relation information indicates the relations of the logic switches on the ladder diagram; a parameter retrieval module, respectively retrieving parameter data corresponding to the logic switches from the machine using the responsive collect commands of the logic switches; and a monitoring module, generating a status of ladder diagram according to the logic switches, the parameter data and the PLC signal address relation information, wherein the status of ladder diagram displays the parameter data corresponding to each logic switch of the ladder diagram when the machine is executing the PLC source program.