There are two properties of incomplete: the incomplete of model definition and causality. With the condition of incomplete model definition, the method of constraint between online observation and the off-line model are proposed to process disordered and undefined events to obtain practical trajectory. Contrast to no being diagnosed by a complete model, this method expands the applicative scope and breaks the model limitation. On condition of causality incomplete, the usage of causal diagram to connect components is proposed. This method solves the halfway diagnostic problem caused by setting models separately, meanwhile enhancing accuracy. It has been tested that the diagnostic way under those two conditions brings out expected results according to certain incomplete models. It also reformulates model partially and improves the model maturity.