Self-reinforced polymer composites (IMSR-SRCs parts) with different structures were prepared by composite injection molding technology and their micro-morphology was observed. The results show that the tensile strength of semi-open IMSR-SRCs parts is increased by 16.89% on average compared with enclosed conventional parts, and the tensile properties of both are better than IMSR-SRCs parts, with a maximum increase of 14.42%. IMSR-SRCs parts show a double "skin-core" structure, and the area ratio of the skin layer is higher than that of conventional parts, and the semi-open type is 5.48% higher than the enclosed IMSR-SRCs parts. The tensile properties are positively related to the area ratio of the skin area. The "shish-kebab" structure was observed by SEM on the skin layer structure of the PLM fusion position. WAXD results show that the crystallinity of the two kinds of IMSR-SRCs parts is not significantly different, and both are lower than the conventional parts, the maximum reduction is 19.23%, and the tensile properties are negatively correlated with the changes in crystallinity. The molecular orientation of the two structures is higher than that of the conventional parts, and the semi-open IMSR-SRCs has a higher orientation, with a maximum improvement of 34.11%. The molecular orientation is positively correlated with the tensile properties of IMSR-SRCs parts. By response surface method, the molecular orientation obtained is the decisive factor affecting the performance of IMSR-SRCs parts. Furthermore, by the least squares minimization program, the dimensionless equations among molding parameters, micro-morphologies and mechanical properties were established, and the prediction of mechanical properties of IMSR-SRCs parts based on microscopic morphology was realized.