This paper explored the warpage which has significant influence on the quality of inject molding for flat micro-mini parts. To control the warpage to an acceptable level, the warpage of a microfluidics plate with a cross-shaped microchannel was researched and the effect of processing parameters on the warpage was considered in detail. First, the generation mechanism and evolution course of the warpage from injection molding was analyzed based on residual stress. Then, the warpage measurement method was established according to simulation technologies and experimental methods. A Si-core based injection mold was designed and fabricated and the optimum processing parameters were obtained with orthogonal experimental method to achieve the minimum warpage. Finally, the quantitative correlations between the warpage and the processing parameters were investigated by extreme difference analysis. Experimental results indicate that the minimum warpage is 141 μm after optimum processing and the sequence of from strong correlation to weak correlation is：holding time, mold temperature, holding pressure, melting temperature and cooling time. The result is helpful to optimize the injection processing of polymer flat micro-mini parts.