The invention relates to a method for detecting secondary consolidation coefficient of soft soil indoors. The method comprises the following steps: (1) placing a vessel on a base, allowing a fulcrum to be contacted with the upper cover of the vessel, and allowing a contact of a sensor to be elastically contacted with the fulcrum; (2) introducing air to a 
piston to jack the vessel and the sensor, lowering the contact in a jacking process to ensure that the contact is constantly contacted with the fulcrum; (3) sending lowered distance 
delta h of the contact to a 
control system after the distance is acquired by the sensor, and calculating the 
void ratio e by a formula, wherein e0 is the natural 
void ratio of soil and constant, h0 is the height when a sample is in zero load; (4) constantly lowering the contact along with 
time extension, calculating the 
void ratio in real time by the 
control system, and finally generating a curve graph of a secondary consolidation coefficient (time logarithm-void ratio), wherein the curve completely comprises an upper curve section, a middle 
linear section and a lower 
linear section; and (5) calculating the slope of the lower 
linear section of the secondary consolidation curve, and calculating the secondary consolidation coefficient Ca. The method ensures that the whole curve is extended by increasing time-taking under each grade of load, and the secondary consolidation segment can more clearly reflect the law that soil body changes along with 
time extension. The final settlement of a building can be calculated according to curve tendency, namely the relationship of basic settlement and time, by combining the service life of the building, the 
engineering stability range can be calculated so as to ensure 
engineering safety.