Abstract: Flowability is a key indicator for assessing the feasibility of flowable construction using freshly mixed solidified sludge, and it is typically evaluated through flowability tests. Research on flowability test standards is an important aspect of promoting flowable construction of freshly mixed solidified sludge. This study investigates the influence of initial water content, cement content, and hydration time on the flowability of sludge and freshly mixed solidified sludge using three mainstream flowability measurement cylinders/conical molds. The study also explores the similarities, differences, and applicability of the flowability patterns reflected by these three measurement molds. The findings of the study are as follows: (1) The flowability of sludge and freshly mixed solidified sludge exhibits maximum/minimum values, and it shows an S-shaped growth with an increase in initial water content. (2) The change in flowability is most significant when the cement content increases from 0 to 50 kg/m³, and the change becomes less pronounced as the cement content continues to increase. When the cement content is fixed, there is a clear linear relationship between water-cement ratio and flowability. The variation patterns of the fitting parameters obtained from the three flowability measurement molds are similar. (3) With the progress of cement hydration, the flowability of freshly mixed solidified sludge decreases, and the decrease is more rapid at higher cement content. (4) The JHS.A 313 and GB/T 2419 flowability measurement cylinders are more closely related to changes in initial water content. The ASTM D6103 flowability measurement cylinder, due to its excessive height, may cause sample tilting during practical operations, while the GB/T 2419 measurement cylinder is more prone to air entrainment. Both factors have a significant impact on the test results. Therefore, it is recommended to use the JHS.A 313 flowability measurement cylinder for the study of sludge and freshly mixed solidified sludge flowability.