Traditional phase noise measuring instruments are expensive, and have complex systems which limit them from being widely used in laboratories and large-scale industrial production tests. So, in this condition, a light and small phase noise measurement system is designed. Based on time-voltage conversion technology and by use of FPGA and single-chip hardware platform, the system can measure the phase-time difference sequence at the rising edge of the zero-crossing point of same frequency signals with small frequency difference and different frequency signals with high precision. According to the autocorrelation algorithm the Fourier transform, the system realizes the conversion of the time-domain phase-time difference sequence into phase noise and provide the display and storage of the test results of phase noise based on the upper computer software. According to final result of the experiment, the system reaches a measurement resolution of time difference sequence of 10-12, and keep a measurement error of phase noise in the offset carrier frequency range of 0～100kHz of less than 5dBc when compared with the PN8010 measuring instrument.