Abstract: A photovoltaic tracking MODBUS LAN broadcast control system was proposed， and Siemens 1200 series PLC was used as the host of MODBUS LAN tracking system.The tracking of the solar altitude angle by the master station was a real-time continuous process， and the master station judged whether the light intensity meted the conditions for power generation or not. If the conditions for power generation were met， the master station broadcasted a control command to instruct the slave station to drive the PV panels to the position of the strongest light angle； If power generation conditions were not met， then the master station did not send control commands to the slave station， and the slave PV panels remained motionless.The Siemens 1200 series PLC master controller completed the measurement and tracking of the solar altitude angle， and was not responsible for driving the PV panel， which basically belongs to zero-load operation. This system reduced the tracking cost of PV panels， improved the tracking accuracy， and eliminated the solar tracking energy consumption of slave PV panels that do not meet the power generation conditions.