The invention relates to the filed of mobile communication, in particular to a technology for time synchronization in the communication system. The invention provides a communication system and a time synchronization method in the system and OTN equipment. The time synchronization method comprises the following steps: acquiring time information from a clock source by the OTN main equipment; carrying out the time synchronization on the OTN slave equipment according to the time information of the OTN main equipment; carrying out the time synchronization on MSTP/PTN equipment connected with the OTN equipment in a gathering layer according to the time information output by the OTN equipment connected with the MSTP/PTN equipment in the gathering layer; and carrying out the time synchronizationon other MSTP/PTN equipment in the gathering layer according to the time information of the MSTP/PTN equipment connected with the OTN equipment. By carrying out the time synchronization on the OTN equipment and then the synchronization on the MSTP or PTN equipment in the gathering layer according to the time of the OTN equipment, the invention can realize the time synchronization of each equipment in a plurality of gathering layers by adopting one clock source, reduces the cost of time synchronization and is convenient for entire network equipment to synchronize a time source.