To alleviate the effect of solar radiation fluctuation on solar thermochemical reaction, phase change material (PCM) is applied in solar-chemical reactor to buffer the temperature vibration induced by solar radiation fluctuation. In order to comprehensively study the effect of PCM on chemical reactor, a two-dimensional model was employed to compare the steady performance of 3 different kinds of solar parabolic trough receiver reactors (SPTRR): without PCM (SPTRR0), with PCM near the outer wall (SPTRR1) and with PCM in the center (SPTRR2). Then, the transient performance of three SPTRRs under continuously pulsed solar radiation and real solar radiation fluctuation are, respectively, analyzed. The results showed that comparable chemical performance can be achieved for all three different SPTRRs although the amount of catalysts in SPTRR1 and SPTRR2 are 13.2% less than that in SPTRR0. When the time interval of cloud presence is 3 min, compared with SPTRR0, the averaged methanol conversions in SPTRR1 and SPTRR2 are, respectively, improved by 10.5 and 9.8% and production selectivity (higher H2/CO) is better. And when under a real solar radiation fluctuation, compared to SPTRR0, the averaged methanol conversions in SPTRR1 and SPTRR2 are relatively improved by about 10.7% and 7.2%. SPTRR1 can more effectively attenuate the effect of solar radiation fluctuation and shows better chemical performance than SPTRR2.