Remote monitoring systems for remotely monitoring execution status of a PLC (Programmable Logic controller) program of a machine include a storage module, a parameter retrieval module and a monitoring module. The storage module stores ladder diagram information corresponding to a PLC source program, wherein the ladder diagram information includes PLC signal address relation information, a plurality of logic switches and a responsive collect command of each logic switch of a ladder diagram. The PLC signal address relation information indicates the relations of the logic switches on the ladder diagram. The parameter retrieval module respectively retrieves parameter data corresponding to the logic switches using the responsive collect commands. The monitoring module generates a status of ladder diagram according to the logic switches, the parameter data and the PLC signal address relation information to display the parameter data corresponding to each logic switch when the machine is executing the PLC source program.