The main purpose of the research was development of a method-based approach and software for the assessment of the effectiveness and efficiency of OSH management system in the company through a predictive model for the assessment of the correlation of an accident risk and generalized desirability indicator based on Harrington function. OSH management system status in a company is proposed to be assessed using mathematical methods for the processing of individual indicators and calculating generalized desirability indicator based on Harrington “desirability curve”. It is proposed to use an expert approach in order to determine individual indicators and assess their weight. It is suggested that such mathematical values as additive synthesizing function, weighted arithmetic mean, multiplicative synthesizing function, weighted geometric mean, should be calculated in «Е2» software. A methodology approach was developed involving mathematical processing of data in various source formats (shares, per cent, numbers, and words) so that Harrington “desirability curve” can be used to assess OSH management system effectiveness and efficacy in the company. A C# software code was developed to import and export Microsoft Excel data which significantly simplifies software use. A predictive model was developed showing the correlation between a professional accident risk value and generalized desirability indicator