Abstract: In China Experimental Fast Reactor (CEFR), the core reactivity will change when pressure of the main container covering gas and coolant flow rate of the first circuit change, which are so-called pressure reactivity and coolant flow rate reactivity effect. The measurement of these two reactivity effects and preliminary error analysis were carried out in CEFR physic startup experiment. The classical period method and inverse kinetic method were used to measure reactivity. The results show that about +20 pcm reactivity will be introduced when the pressure of main container covering gas increases from 5 kPa to 50 kPa, which means the CEFR pressure reactivity is positive, and about -49 pcm reactivity will be introduced when the main pump speed increases from 150 r/min to 989 r/min, which means the CEFR coolant flow rate reactivity is negative. The results from period method agree well with that from inverse kinetic method. According to the preliminary error analysis, the error of test result is dominated by measuring error of coolant temperature.