The invention provides a 1/2-period frequency measuring system and method. The frequency measuring system comprises a fundamental wave generating module, a high-frequency pulse counting module and a control processing module, wherein the fundamental wave generating module is used for generating a gate signal through frequency multiplication/frequency division according to an external clock of a programmable device; the high-frequency pulse counting module is used for counting the high-frequency pulse signals according to the positive half cycle of the gate signal; and the control processing module is used for sequentially sending out a high-frequency pulse number signal in each period according to a reading command. The method comprises the following steps: in frequency measurement, the fundamental wave generating module generates the gate signal through frequency multiplication/frequency division according to the external clock of the programmable device; high-frequency pulse signals are filtered and enter the high-frequency pulse counting module; the high-frequency pulse counting module counts the filtered high-frequency pulse signals according to the positive half cycle of the gate signal to sequentially obtain the pulse numbers of the positive half cycles of different periods, and sends the pulse numbers to the control processing module; and finally, the control processing module sequentially sends out the high-frequency pulse signals in each period according to the generated reading command.