Good temporal coherence is a significant advantage of the seeding free electron laser(FEL) compare with FEL of the self-amplified spontaneous emission(SASE) type.The temporal coherence properties of HGHG (high-gain harmonic generation) pulses on the Shanghai Deep Ultra-violate FEL at Shanghai Institute of Applied Physics are measured at 600 nm and 400 nm(the wavelength of seed laser is 1200 nm) by a Michelson interferometer with sub-femto second time resolution.At zero delay visibilities of 0.88±0.02 at 600 nm and 0.66±0.06 at 400 nm are measured.The delay of one partial beam reveals coherence time of 119±6.7 fs at 600nm and 112±16.9 fs at 400 nm.