To investigate the effects of different sand rates and aggregate sizes on the fracture toughness of plastic concrete, mechanical property tests and three-point bending notched beam fracture tests were conducted to analyze the physical and mechanical properties and apparent morphology of plastic concrete with different mix ratios. The evolution of fracture toughness of plastic concrete with different sand rates and aggregate sizes was revealed. The results show that the strength and fracture toughness of plastic concrete with different sand rates and aggregate sizes vary significantly. With an increase in the sand content from 45% to 85%, the strength and fracture toughness of plastic concrete exhibit a noticeable decline and an upward trend for aggregate particle sizes in the range of 0 to 5 mm and 5 to 10 mm, respectively, but the variation in fracture toughness is comparatively lower. For aggregate particle sizes ranging from 10 to 20 mm, the specimen strength variation law is comparable to that observed for particle sizes between 5 and 10 mm, with a general upward tendency. With an increase in the sand content from 45% to 85%, the fracture toughness first decreases and then increases. The changes in strength, characteristic load, and fracture toughness of plastic concrete under the same mix ratio conditions are relatively consistent with the variation of aggregate particle size.