Heat removal capacity of slot synthetic jet impinging on target plate with constant heat flux is numerically studied in this work. The signal of synthetic jet velocity is rectangular waveform; parameters investigated cover dimensionless jet-to-surface distance H/w=2 and 4, Reynolds number Re 10,000 – 20,000, oscillating frequency f 10 Hz – 20 Hz, and corresponding Strouhal number St of 0.1598. The results indicated that heat transfer rate of synthetic jet at H/w=4 is higher than that at H/w=2 with other conditions unchanged, which is attributed to the discrepancy between flow structures. The extent of Nusselt number Nu enhancement as a result of Re promotion, increases with H/w. Moreover, under the circumstance of rectangular waveform and identical H/w, the similarity of area-averaged Nusselt number variation process emerges under the same St that roots in the comparability of flow field evolution.