Abstract: The fissure of soft rock of Mesozoic era and Cenozoic era isn’t developmental normally. But there exist many pores in this rock and the cementation intensity of this rock is very low. Easy disturbance is notable. Mechanics parameters are valued after rebating test result of rock block. It makes mechanics index of weak foundation to be greatly lower than actual value. This is a bemusement in the field of engineering at present. The research result from several engineering illustrations shows that soft rock mass of Mesozoic era and Cenozoic era is different from the rock mass with many fissures. At the same time，the rock block possesses anti-size effect compared with test result in situ：The proportional limit value of rock mass of load test in situ is normally more than 1.62-20 times Rc. The ultimate intensity value of rock mass of load test in situ is more than 2.4-50 times Rc. The test parameter value of lateral frictional resistance of pile is obviously increased. Rc value is also increased obviously by reduction method in current code. The modulus of deformation of badly soft rock in situ is more than the test value of rock block. Actually measured Kv is more than 1 generally. Grading rock mass is classified by Rc according to BQ method. Base quality index isn’t calculated directly by measured Kv.Kv reflects mainly low hardness and disturbing characteristic of soft rock in view of physics meaning. The performance of soft rock in situ（namely keeping its crude structure）and state are the key that soft rock keeps mechanics property. So，the mechanics test of rock mass in situ is the obligatory choice to study deformation property，bearing capacity of foundation（end bearing of pile），and lateral ultimate friction resistance of pile. More test methods are boosted to reach standardization on the basis of ripe experience and a lot of engineering examples.