Size effect is the inherent characteristic of cementitious materials, which is related to the factors such as mixture ratio, strength and structure composition. The High toughness cementitious composite is a new type of composite material with excellent toughness, but at the same time the structure of it is quite different from that of ordinary concrete. However, most of the current studies on size effects are limited to ordinary concrete and high-strength concrete, and there is no relevant standard to regulate the size effect of high toughness cementitious composite. In order to explore the compressive strength size effect of high toughness cementitious composite, the uniaxial compressive tests and orthogonal analysis on 16 groups of high toughness cementitious composites with different ratios and two sizes of cube specimens were carried out to study the influence of four factors including fiber content, water-binder ratio, fly ash content and sand-binder ratio on the compressive strength size effect of this material. The test results show that the brittleness of high toughness cementitious composite is obviously reduced compared with ordinary concrete. The primary and secondary order of the influence of this four factors on size effect is water-binder ratio > fiber content > fly ash content > sand-binder ratio; the influence of water-binder ratio and fiber content is highly significant, while sand-binder ratio has little effect on the size effect